Primality by trial division

Write a boolean function that tells whether a given integer is prime.

Task
Primality by trial division
You are encouraged to solve this task according to the task description, using any language you may know.
Task


Remember that   1   and all non-positive numbers are not prime.

Use trial division.

Even numbers greater than   2   may be eliminated right away.

A loop from   3   to    n    will suffice,   but other loops are allowed.


Related tasks



11l

F is_prime(n)
   I n < 2
      R 0B
   L(i) 2..Int(sqrt(n))
      I n % i == 0
         R 0B
   R 1B

360 Assembly

*        Primality by trial division  26/03/2017
PRIMEDIV CSECT
         USING  PRIMEDIV,R13       base register
         B      72(R15)            skip savearea
         DC     17F'0'             savearea
         STM    R14,R12,12(R13)    save previous context
         ST     R13,4(R15)         link backward
         ST     R15,8(R13)         link forward
         LR     R13,R15            set addressability
         LA     R10,PG             pgi=0
         LA     R6,1               i=1
       DO WHILE=(C,R6,LE,=F'50')   do i=1 to 50
         LR     R1,R6                i
         BAL    R14,ISPRIME          call isprime(i)
       IF C,R0,EQ,=F'1' THEN         if isprime(i) then
         XDECO  R6,XDEC                edit i
         MVC    0(4,R10),XDEC+8        output i
         LA     R10,4(R10)             pgi+=4
       ENDIF    ,                    endif
         LA     R6,1(R6)             i++
       ENDDO    ,                  enddo i
         XPRNT  PG,L'PG            print buffer
         L      R13,4(0,R13)       restore previous savearea pointer
         LM     R14,R12,12(R13)    restore previous context
         XR     R15,R15            rc=0
         BR     R14                exit
*------- ----   ----------------------------------------
ISPRIME  EQU    *                  function isprime(n)
       IF C,R1,LE,=F'1' THEN       if n<=1 then
         LA     R0,0                 return(0)
         BR     R14                  return
       ENDIF    ,                  endif
       IF C,R1,EQ,=F'2' THEN       if n=2 then
         LA     R0,1                 return(1)
         BR     R14                  return
       ENDIF    ,                  endif
         LR     R4,R1              n
         N      R4,=X'00000001'    n and 1
       IF LTR,R4,Z,R4 THEN         if mod(n,2)=0 then
         LA     R0,0                 return(0)
         BR     R14                  return
       ENDIF    ,                  endif
         LA     R7,3               j=3
         LA     R5,9               r5=j*j
       DO WHILE=(CR,R5,LE,R1)      do j=3 by 2 while j*j<=n
         LR     R4,R1                n
         SRDA   R4,32                ~
         DR     R4,R7                /j
       IF LTR,R4,Z,R4 THEN           if mod(n,j)=0 then
         LA     R0,0                   return(0)
         BR     R14                    return
       ENDIF    ,                    endif
         LA     R7,2(R7)             j+=2
         LR     R5,R7                j
         MR     R4,R7                r5=j*j
       ENDDO    ,                  enddo j
         LA     R0,1               return(1)
         BR     R14                return
*------- ----   ----------------------------------------
PG       DC     CL80' '            buffer
XDEC     DS     CL12               temp for xdeco
         YREGS
         END    PRIMEDIV
Output:
  2   3   5   7  11  13  17  19  23  29  31  37  41  43  47

68000 Assembly

isPrime:
; REG USAGE:
; D0 = input (unsigned 32-bit integer)
; D1 = temp storage for D0
; D2 = candidates for possible factors
; D3 = temp storage for quotient/remainder
; D4 = total count of proper divisors.

MOVEM.L D1-D4,-(SP)      ;push data regs except D0
MOVE.L #0,D1
MOVEM.L D1,D2-D4         ;clear regs D1 thru D4

CMP.L #0,D0
BEQ notPrime
CMP.L #1,D0
BEQ notPrime
CMP.L #2,D0
BEQ wasPrime

MOVE.L D0,D1            ;D1 will be used for temp storage.
AND.L #1,D1             ;is D1 even?
BEQ notPrime            ;if so, it's not prime!

MOVE.L D0,D1            ;restore D1

MOVE.L #3,D2		;start with 3

computeFactors:
DIVU D2,D1              ;remainder is in top 2 bytes, quotient in bottom 2.
MOVE.L D1,D3		;temporarily store into D3 to check the remainder
SWAP D3			;swap the high and low words of D3. Now bottom 2 bytes contain remainder.
CMP.W #0,D3		;is the bottom word equal to 0?
BNE D2_Wasnt_A_Divisor	;if not, D2 was not a factor of D1.

ADDQ.L #1,D4            ;increment the count of proper divisors.
CMP.L #2,D4             ;is D4 two or greater?
BCC notPrime            ;if so, it's not prime! (Ends early. We'll need to check again if we made it to the end.)

D2_Wasnt_A_Divisor:
MOVE.L D0,D1            ;restore D1.
ADDQ.L #1,D2		;increment D2


CMP.L D2,D1             ;is D2 now greater than D1?
BLS computeFactors      ;if not, loop again

CMP.L #1,D4		;was there only one factor?
BEQ wasPrime		;if so, D0 was prime.

notPrime:
MOVE.L #0,D0             ;return false
MOVEM.L (SP)+,D1-D4      ;pop D1-D4
RTS

wasPrime:
MOVE.L #1,D0             ;return true
MOVEM.L (SP)+,D1-D4      ;pop D1-D4
RTS
;end of program

AArch64 Assembly

Works with: as version Raspberry Pi 3B version Buster 64 bits
/* ARM assembly AARCH64 Raspberry PI 3B */
/*  program testPrime64.s   */

/*******************************************/
/* Constantes file                         */
/*******************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc"

/*******************************************/
/* Initialized data */
/*******************************************/
.data
szMessStartPgm:            .asciz "Program start \n"
szMessEndPgm:              .asciz "Program normal end.\n"
szMessNotPrime:            .asciz "Not prime.\n"
szMessPrime:               .asciz "Prime\n"
szCarriageReturn:          .asciz "\n"

/*******************************************/
/* UnInitialized data                      */
/*******************************************/
.bss 
.align 4
/*******************************************/
/*  code section                           */
/*******************************************/
.text
.global main 
main:                                           // program start
    ldr x0,qAdrszMessStartPgm                   // display start message
    bl affichageMess
    ldr x0,qVal
    bl isPrime                                  // test prime ?
    cmp x0,#0
    beq 1f
    ldr x0,qAdrszMessPrime                      // yes
    bl affichageMess
    b 2f
1:
    ldr x0,qAdrszMessNotPrime                   // no 
    bl affichageMess
2:

    ldr x0,qAdrszMessEndPgm                     // display end message
    bl affichageMess

100:                                            // standard end of the program
    mov x0,0                                    // return code
    mov x8,EXIT                                 // request to exit program
    svc 0                                       // perform system call
qAdrszMessStartPgm:        .quad szMessStartPgm
qAdrszMessEndPgm:          .quad szMessEndPgm
qAdrszCarriageReturn:      .quad szCarriageReturn
qAdrszMessNotPrime:        .quad szMessNotPrime
qAdrszMessPrime:           .quad szMessPrime
//qVal:                      .quad 1042441       // test not prime
//qVal:                      .quad 1046527       // test prime
//qVal:                       .quad 37811          // test prime 
//qVal:                      .quad 1429671721    // test not prime (37811 * 37811)
qVal:                      .quad 100000004437    // test prime
/******************************************************************/
/*     test if number is prime                                    */ 
/******************************************************************/
/* x0 contains the number  */
/* x0 return 1 if prime else return 0 */
isPrime:
    stp x1,lr,[sp,-16]!        // save  registers
    cmp x0,1                   // <= 1 ?
    ble 98f
    cmp x0,3                   // 2 and 3 prime
    ble 97f 
    tst x0,1                   //  even ?
    beq 98f 
    mov x11,3                 // first divisor
1:
    udiv x12,x0,x11
    msub x13,x12,x11,x0       // compute remainder
    cbz x13,98f               // end if zero
    add x11,x11,#2            // increment divisor
    cmp x11,x12               // divisors<=quotient ?
    ble 1b                    // loop
97:
    mov x0,1                  // return prime
    b 100f
98:
    mov x0,0                  // not prime
    b 100f
100:
    ldp x1,lr,[sp],16         // restaur  2 registers
    ret                       // return to address lr x30

/********************************************************/
/*        File Include fonctions                        */
/********************************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeARM64.inc"

ABAP

class ZMLA_ROSETTA definition
  public
  create public .

public section.

  types:
    enumber         TYPE          N  LENGTH 60 .
  types:
    listof_enumber  TYPE TABLE OF enumber .

  class-methods IS_PRIME
    importing
      value(N) type ENUMBER
    returning
      value(OFLAG) type ABAP_BOOL .
  class-methods IS_PRIME_I
    importing
      value(N) type I
    returning
      value(OFLAG) type ABAP_BOOL .
  protected section.
  private section.
ENDCLASS.



CLASS ZMLA_ROSETTA IMPLEMENTATION.


* <SIGNATURE>---------------------------------------------------------------------------------------+
* | Static Public Method ZMLA_ROSETTA=>IS_PRIME
* +-------------------------------------------------------------------------------------------------+
* | [--->] N                              TYPE        ENUMBER
* | [<-()] OFLAG                          TYPE        ABAP_BOOL
* +--------------------------------------------------------------------------------------</SIGNATURE>
  method IS_PRIME.
    IF n < 2.
      oflag = abap_false.
      RETURN.
    ENDIF.
    IF n = 2 or n = 3.
      oflag = abap_true.
      RETURN.
    ENDIF.
    IF n mod 2 = 0 or n mod 3 = 0.
      oflag = abap_false.
      RETURN.
    ENDIF.
    DATA: lim type enumber,
          d   type enumber,
          i   TYPE i        VALUE 2.
    lim = sqrt( n ).
    d   = 5.
    WHILE d <= lim.
      IF n mod d = 0.
        oflag = abap_false.
        RETURN.
      ENDIF.
      d = d + i.
      i = 6 - i.  " this modifies 2 into 4 and viceversa
    ENDWHILE.
    oflag = abap_true.
    RETURN.
  endmethod.


* <SIGNATURE>---------------------------------------------------------------------------------------+
* | Static Public Method ZMLA_ROSETTA=>IS_PRIME_I
* +-------------------------------------------------------------------------------------------------+
* | [--->] N                              TYPE        I
* | [<-()] OFLAG                          TYPE        ABAP_BOOL
* +--------------------------------------------------------------------------------------</SIGNATURE>
  method IS_PRIME_I.
    IF n < 2.
      oflag = abap_false.
      RETURN.
    ENDIF.
    IF n = 2 or n = 3.
      oflag = abap_true.
      RETURN.
    ENDIF.
    IF n mod 2 = 0 or n mod 3 = 0.
      oflag = abap_false.
      RETURN.
    ENDIF.
    DATA: lim type i,
          d   type i,
          i   TYPE i        VALUE 2.
    lim = sqrt( n ).
    d   = 5.
    WHILE d <= lim.
      IF n mod d = 0.
        oflag = abap_false.
        RETURN.
      ENDIF.
      d = d + i.
      i = 6 - i.  " this modifies 2 into 4 and viceversa
    ENDWHILE.
    oflag = abap_true.
    RETURN.
  endmethod.
ENDCLASS.

ACL2

(defun is-prime-r (x i)
   (declare (xargs :measure (nfix (- x i))))
   (if (zp (- (- x i) 1))
       t
       (and (/= (mod x i) 0)
            (is-prime-r x (1+ i)))))

(defun is-prime (x)
   (or (= x 2)
       (is-prime-r x 2)))

Action!

BYTE FUNC IsPrime(CARD a)
  CARD i

  IF a<=1 THEN
    RETURN (0)
  FI
  
  FOR i=2 TO a/2
  DO
    IF a MOD i=0 THEN
      RETURN (0)
    FI
  OD
RETURN (1)

PROC Test(CARD a)
  IF IsPrime(a) THEN
    PrintF("%I is prime%E",a)
  ELSE
    PrintF("%I is not prime%E",a)
  FI
RETURN

PROC Main()
  Test(13)
  Test(997)
  Test(1)
  Test(6)
  Test(120)
  Test(0)
RETURN
Output:

Screenshot from Atari 8-bit computer

13 is prime
997 is prime
1 is not prime
6 is not prime
120 is not prime
0 is not prime

ActionScript

function isPrime(n:int):Boolean
{
	if(n < 2) return false;
	if(n == 2) return true;
	if((n & 1) == 0) return false;
	for(var i:int = 3; i <= Math.sqrt(n); i+= 2)
		if(n % i == 0) return false;
	return true;
}

Ada

function Is_Prime(Item : Positive) return Boolean is
   Test : Natural;
begin
   if Item = 1 then
      return False;
   elsif Item = 2 then
      return True;
   elsif Item mod 2 = 0 then
      return False;
   else
      Test := 3;
      while Test <= Integer(Sqrt(Float(Item))) loop
         if Item mod Test = 0 then
            return False;
         end if;
         Test := Test + 2;
      end loop;
   end if;
   return True;
end Is_Prime;

Sqrt is made visible by a with / use clause on Ada.Numerics.Elementary_Functions.

With Ada 2012, the function can be made more compact as an expression function (but without loop optimized by skipping even numbers) :

function Is_Prime(Item : Positive) return Boolean is
   (Item /= 1 and then
    (for all Test in 2..Integer(Sqrt(Float(Item))) => Item mod Test /= 0));

As an alternative, one can use the generic function Prime_Numbers.Is_Prime, as specified in Prime decomposition#Ada, which also implements trial division.

with Prime_Numbers; 

procedure Test_Prime is

   package Integer_Numbers is new 
     Prime_Numbers (Natural, 0, 1, 2); 
   use Integer_Numbers;

begin
   if Is_Prime(12) or (not Is_Prime(13)) then 
      raise Program_Error with "Test_Prime failed!";
   end if;
end Test_Prime;

ALGOL 60

Works with: A60
begin

boolean procedure isprime(n);
value n; integer n;
begin
    comment - local procedure tests whether n is even;
    boolean procedure even(n);
    value n; integer n;
    even := entier(n / 2) * 2 = n;

    if n < 2 then 
        isprime := false
    else if even(n) then 
        isprime := (n = 2)
    else
        begin
           comment - check odd divisors up to sqrt(n);
           integer i, limit;
           boolean divisible;
           i := 3;
           limit := entier(sqrt(n));
           divisible := false;
           for i := i while i <= limit and not divisible do 
              begin
                 if entier(n / i) * i = n then
                     divisible := true;
                 i := i + 2
              end;          
           isprime := if divisible then false else true;
        end;
end;

comment - exercise the procedure;
integer i;
outstring(1,"Testing first 50 numbers for primality:\n");         
for i := 1 step 1 until 50 do
  if isprime(i) then
      outinteger(1,i);

end
Output:
Testing first 50 numbers for primality:
 2  3  5  7  11  13  17  19  23  29  31  37  41  43  47

ALGOL 68

Works with: ALGOL 68 version Revision 1 - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
COMMENT
  This routine is used in more than one place, and is essentially a
  template that can by used for many different types, eg INT, LONG INT...
USAGE
  MODE ISPRIMEINT = INT, LONG INT, etc
  PR READ "prelude/is_prime.a68" PR
END COMMENT
PROC is prime = ( ISPRIMEINT p )BOOL:
  IF p <= 1 OR ( NOT ODD p AND p/= 2) THEN
    FALSE
  ELSE
    BOOL prime := TRUE;
    FOR i FROM 3 BY 2 TO ENTIER sqrt(p)
      WHILE prime := p MOD i /= 0 DO SKIP OD;
    prime
  FI
main:( 
  INT upb=100;
  printf(($" The primes up to "g(-3)" are:"l$,upb));
  FOR i TO upb DO 
    IF is prime(i) THEN
      printf(($g(-4)$,i))
    FI
  OD;
  printf($l$)
)
Output:
The primes up to 100 are:
  2   3   5   7  11  13  17  19  23  29  31  37  41  43  47  53  59  61  67  71  73  79  83  89  97

ALGOL-M

BEGIN

% RETURN P MOD Q %
INTEGER FUNCTION MOD(P, Q);
INTEGER P, Q;
BEGIN
  MOD := P - Q * (P / Q);
END;

% RETURN INTEGER SQUARE ROOT OF N %
INTEGER FUNCTION ISQRT(N);
INTEGER N;
BEGIN
  INTEGER R1, R2;
  R1 := N;
  R2 := 1;
  WHILE R1 > R2 DO
    BEGIN
      R1 := (R1+R2) / 2;
      R2 := N / R1;
    END;
  ISQRT := R1;
END;

% RETURN 1 IF N IS PRIME, OTHERWISE 0 %
INTEGER FUNCTION ISPRIME(N);
INTEGER N;
BEGIN
  IF N = 2 THEN 
    ISPRIME := 1
  ELSE IF (N < 2) OR (MOD(N,2) = 0) THEN
    ISPRIME := 0
  ELSE % TEST ODD NUMBERS UP TO SQRT OF N %
    BEGIN
      INTEGER I, LIMIT;
      LIMIT := ISQRT(N);
      I := 3;
      WHILE I <= LIMIT AND MOD(N,I) <> 0 DO
        I := I + 2;
      ISPRIME := (IF I <= LIMIT THEN 0 ELSE 1);
    END;
END;  

% TEST FOR PRIMES IN RANGE 1 TO 50 %
INTEGER I;
WRITE("");
FOR I := 1 STEP 1 UNTIL 50 DO
  BEGIN
    IF ISPRIME(I)=1 THEN WRITEON(I,"  "); % WORKS FOR 80 COL SCREEN %
  END;

END
Output:
     2       3       5       7      11      13      17      19      23      29
    31      37      41      43      47

ALGOL W

% returns true if n is prime, false otherwise %
% uses trial division                         %
logical procedure isPrime ( integer value n ) ;
    if n < 3 or not odd( n ) then n = 2
    else begin
        % odd number > 2 %
        integer f, rootN;
        logical havePrime;
        f         := 3;
        rootN     := entier( sqrt( n ) );
        havePrime := true;
        while f <= rootN and havePrime do begin
            havePrime := ( n rem f ) not = 0;
            f         := f + 2
        end;
        havePrime
    end isPrime ;

Test program:

begin
    logical procedure isPrime ( integer value n ) ; algol "isPrime" ;
    for i := 0 until 32 do if isPrime( i ) then writeon( i_w := 1,s_w := 1, i )
end.
Output:
2 3 5 7 11 13 17 19 23 29 31

APL

prime  2=0+.=⍳|⊣
Output:
      ((/⍨)prime¨)100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

AppleScript

on isPrime(n)
    if (n < 3) then return (n is 2)
    if (n mod 2 is 0) then return false
    repeat with i from 3 to (n ^ 0.5) div 1 by 2
        if (n mod i is 0) then return false
    end repeat
    
    return true
end isPrime

-- Test code:
set output to {}
repeat with n from -7 to 100
    if (isPrime(n)) then set end of output to n
end repeat
return output

Or eliminating multiples of 3 at the start as well as those of 2:

on isPrime(n)
    if (n < 4) then return (n > 1)
    if ((n mod 2 is 0) or (n mod 3 is 0)) then return false
    repeat with i from 5 to (n ^ 0.5) div 1 by 6
        if ((n mod i is 0) or (n mod (i + 2) is 0)) then return false
    end repeat
    
    return true
end isPrime

-- Test code:
set output to {}
repeat with n from -7 to 100
    if (isPrime(n)) then set end of output to n
end repeat
return output
Output:
{2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97}

ARM Assembly

Works with: as version Raspberry Pi
or android 32 bits with application Termux
/* ARM assembly Raspberry PI  */
/*  program testtrialprime.s   */

/************************************/
/* Constantes                       */
/************************************/
/* for this file see task include a file in language ARM assembly*/
.include "../constantes.inc"

//.include "../../ficmacros32.inc"       @ for debugging developper
/************************************/
/* Initialized data                 */
/************************************/
.data
szMessPrime:          .asciz " is prime.\n"
szMessNotPrime:       .asciz " is not prime.\n"
szCarriageReturn:     .asciz "\n"
szMessStart:          .asciz "Program 32 bits start.\n"
/************************************/
/* UnInitialized data               */
/************************************/
.bss 
sZoneConv:            .skip 24
/************************************/
/*  code section                    */
/************************************/
.text
.global main 
main:                        @ entry of program
    ldr r0,iAdrszMessStart
    bl affichageMess
    mov r0,#19
    bl testPrime
    
    ldr r0,iStart            @ number 
    bl testPrime
    ldr r0,iStart1           @ number 
    bl testPrime
 
100:                         @ standard end of the program
    mov r0, #0               @ return code
    mov r7, #EXIT            @ request to exit program
    swi 0                    @ perform the system call
iAdrsZoneConv:             .int sZoneConv

iAdrszMessPrime:         .int szMessPrime
iAdrszMessNotPrime:      .int szMessNotPrime
iAdrszCarriageReturn:     .int szCarriageReturn
iAdrszMessStart:          .int szMessStart
iStart:                   .int 2600002183
iStart1:                  .int 4124163031
/******************************************************************/
/*     test if number is prime                                    */ 
/******************************************************************/
/* r0 contains the number  */
testPrime:
    push {r1,r2,lr}                @ save  registers 
    mov r2,r0
    ldr r1,iAdrsZoneConv
    bl conversion10          @ decimal conversion
    ldr r0,iAdrsZoneConv
    bl affichageMess
    mov r0,r2
    bl isPrime
    cmp r0,#0
    beq 1f
    ldr r0,iAdrszMessPrime
    bl affichageMess
    b 100f
1:  
    ldr r0,iAdrszMessNotPrime
    bl affichageMess 
100:
    pop {r1,r2,pc}                 @ restaur registers
/******************************************************************/
/*     test if number is prime                                    */ 
/******************************************************************/
/* r0 contains the number  */
/* r0 return 1 if prime else return 0 */
isPrime:
    push {r4,lr}                @ save  registers 
    cmp r0,#1                   @ <= 1 ?
    movls r0,#0                 @ not prime
    bls 100f
    cmp r0,#3                   @ 2 and 3 prime
    movls r0,#1
    bls 100f
    tst r0,#1                   @  even ?
    moveq r0,#0                 @ not prime
    beq 100f
    mov r4,r0                   @ save number
    mov r1,#3                   @ first divisor
1:
    mov r0,r4                   @ number
    bl division
    add r1,r1,#2                @ increment divisor
    cmp r3,#0                   @ remainder = zero ?
    moveq r0,#0                 @ not prime
    beq 100f   
    cmp r1,r2                   @ divisors<=quotient ?
    ble 1b                      @ loop
    mov r0,#1                   @ return prime

100:
    pop {r4,pc}                 @ restaur registers
/***************************************************/
/*      ROUTINES INCLUDE                           */
/***************************************************/
/* for this file see task include a file in language ARM assembly*/
.include "../affichage.inc"
Output:
Program 32 bits start.
19          is prime.
2600002183  is prime.
4124163031  is not prime.

Arturo

isPrime?: function [n][
    if n=2 -> return true
    if n=3 -> return true
    if or? n=<1 0=n%2 -> return false
 
    high: to :integer sqrt n
    loop high..2 .step: 3 'i [
    	if 0=n%i -> return false
    ]

    return true
]
 
loop 1..20 'i [
    print ["isPrime?" i "=" isPrime? i ]
]
Output:
isPrime? 1 = false 
isPrime? 2 = true 
isPrime? 3 = true 
isPrime? 4 = false 
isPrime? 5 = true 
isPrime? 6 = false 
isPrime? 7 = true 
isPrime? 8 = false 
isPrime? 9 = false 
isPrime? 10 = false 
isPrime? 11 = true 
isPrime? 12 = false 
isPrime? 13 = true 
isPrime? 14 = false 
isPrime? 15 = false 
isPrime? 16 = false 
isPrime? 17 = true 
isPrime? 18 = false 
isPrime? 19 = true 
isPrime? 20 = false

AutoHotkey

Discussion

MsgBox % IsPrime(1995937) 
Loop 
   MsgBox % A_Index-3 . " is " . (IsPrime(A_Index-3) ? "" : "not ") . "prime." 

IsPrime(n,k=2) { ; testing primality with trial divisors not multiple of 2,3,5, up to sqrt(n) 
   d := k+(k<7 ? 1+(k>2) : SubStr("6-----4---2-4---2-4---6-----2",Mod(k,30),1)) 
   Return n < 3 ? n>1 : Mod(n,k) ? (d*d <= n ? IsPrime(n,d) : 1) : 0 
}

AutoIt

#cs ----------------------------------------------------------------------------

 AutoIt Version: 3.3.8.1
 Author:         Alexander Alvonellos


 Script Function:
	Perform primality test on a given integer $number.
	RETURNS: TRUE/FALSE

#ce ----------------------------------------------------------------------------
Func main()
	ConsoleWrite("The primes up to 100 are: " & @LF)
	For $i = 1 To 100 Step 1
		If(isPrime($i)) Then
			If($i <> 97) Then
				ConsoleWrite($i & ", ")
			Else
				ConsoleWrite($i)
			EndIf
		EndIf
	Next
EndFunc

Func isPrime($n)
	If($n < 2) Then Return False
	If($n = 2) Then Return True
	If(BitAnd($n, 1) = 0) Then Return False
	For $i = 3 To Sqrt($n) Step 2
		If(Mod($n, $i) = 0) Then Return False
	Next
	Return True
EndFunc
main()

AWK

$ awk 'func prime(n){for(d=2;d<=sqrt(n);d++)if(!(n%d)){return 0};return 1}{print prime($1)}'

Or more legibly, and with n <= 1 handling

function prime(n) {
    if (n <= 1) return 0
    for (d = 2; d <= sqrt(n); d++)
        if (!(n % d)) return 0
    return 1
}

{print prime($1)}

B

B as on PDP7/UNIX0

Translation of: C
Works with: B as on PDP7/UNIX0 version (proto-B?)
isprime(n) {
  auto p;
  if(n<2) return(0);
  if(!(n%2)) return(n==2);
  p=3;
  while(n/p>p) {
    if(!(n%p)) return(0);
    p=p+2;
  }
  return(1);
}

BASIC

Applesoft BASIC

 100  DEF  FN MOD(NUM) = NUM -  INT (NUM / DIV) * DIV: REM NUM MOD DIV
 110  FOR I = 1 TO 99
 120      V = I: GOSUB 200"ISPRIME
 130      IF ISPRIME THEN  PRINT " "I;
 140  NEXT I
 150  END
 
 200  ISPRIME = FALSE: IF V < 2 THEN  RETURN 
 210  DIV = 2:ISPRIME =  FN MOD(V): IF  NOT ISPRIME THEN ISPRIME = V = 2: RETURN 
 220  LIMIT =  SQR (V): IF LIMIT >  = 3 THEN  FOR DIV = 3 TO LIMIT STEP 2:ISPRIME =  FN MOD(V): IF ISPRIME THEN  NEXT DIV
 230  RETURN

BASIC256

Translation of: FreeBASIC
for i = 1 to 99
    if isPrime(i) then print string(i); " "; 
next i
end

function isPrime(v)
    if v < 2 then return False
    if v mod 2 = 0 then return v = 2
    if v mod 3 = 0 then return v = 3
    d = 5
    while d * d <= v
        if v mod d = 0 then return False else d += 2
    end while
    return True
end function

BBC BASIC

      FOR i% = -1 TO 100
        IF FNisprime(i%) PRINT ; i% " is prime"
      NEXT
      END
      
      DEF FNisprime(n%)
      IF n% <= 1 THEN = FALSE
      IF n% <= 3 THEN = TRUE
      IF (n% AND 1) = 0 THEN = FALSE
      LOCAL t%
      FOR t% = 3 TO SQR(n%) STEP 2
        IF n% MOD t% = 0 THEN = FALSE
      NEXT
      = TRUE
Output:
2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime

Craft Basic

for i = 1 to 50

	if i < 2 then

		let p = 0

	else

		if i = 2 then

			let p = 1

		else

			if i % 2 = 0 then

				let p = 0

			else

				let p = 1

				for j = 3 to int(i ^ .5) step 2

					if i % j = 0 then

						let p = 0
						break j

					endif

					wait

				next j

			endif

		endif

	endif

	if p <> 0 then

		print i

	endif

next i
Output:
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 

FBSL

The second function (included by not used) I would have thought would be faster because it lacks the SQR() function. As it happens, the first is over twice as fast.

#APPTYPE CONSOLE

FUNCTION ISPRIME(n AS INTEGER) AS INTEGER
    IF n = 2 THEN
        RETURN TRUE
    ELSEIF n <= 1 ORELSE n MOD 2 = 0 THEN
        RETURN FALSE
    ELSE
        FOR DIM i = 3 TO SQR(n) STEP 2
            IF n MOD i = 0 THEN
                RETURN FALSE
            END IF
        NEXT
        RETURN TRUE
    END IF
END FUNCTION

FUNCTION ISPRIME2(N AS INTEGER) AS INTEGER
    IF N <= 1 THEN RETURN FALSE
    DIM I AS INTEGER = 2
    WHILE I * I <= N
        IF N MOD I = 0 THEN
            RETURN FALSE
        END IF
        I = I + 1
    WEND
    RETURN TRUE
END FUNCTION

' Test and display primes 1 .. 50
DIM n AS INTEGER

FOR n = 1 TO 50
    IF ISPRIME(n) THEN
        PRINT n, " ";
    END IF
NEXT

PAUSE
Output:
 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47
 Press any key to continue...

FreeBASIC

' FB 1.05.0 Win64

Function isPrime(n As Integer) As Boolean
  If n < 2 Then Return False
  If n = 2 Then Return True
  If n Mod 2  = 0 Then Return False
  Dim limit As Integer = Sqr(n)
  For i As Integer = 3 To limit Step 2
    If n Mod i = 0 Then Return False
  Next
  Return True
End Function

' To test this works, print all primes under 100
For i As Integer = 1 To 99
  If isPrime(i) Then 
    Print Str(i); " "; 
  End If
Next

Print : Print
Print "Press any key to quit"
Sleep
Output:
 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

FutureBasic

window 1, @"Primality By Trial Division", (0,0,480,270)

local fn isPrime( n as long ) as Boolean
  long    i
  Boolean result
  
  if n < 2 then result = NO : exit fn
  if n = 2 then result = YES : exit fn
  if n mod 2 == 0  then result = NO : exit fn
  
  result = YES
  for i = 3 to int( n^.5 ) step 2
    if n mod i == 0 then result = NO : break
  next i
end fn = result

long i, j = 0

print "Prime numbers between 0 and 1000:"
for i = 0 to 1000
  if ( fn isPrime(i) != _false )
    printf @"%3d\t",i : j++
    if j mod 10 == 0 then print
  end if
next

HandleEvents
Output:
 Prime numbers between 0 and 1000:
   2     3     5     7    11    13    17    19    23    29   
  31    37    41    43    47    53    59    61    67    71   
  73    79    83    89    97   101   103   107   109   113  
 127   131   137   139   149   151   157   163   167   173  
 179   181   191   193   197   199   211   223   227   229  
 233   239   241   251   257   263   269   271   277   281  
 283   293   307   311   313   317   331   337   347   349  
 353   359   367   373   379   383   389   397   401   409  
 419   421   431   433   439   443   449   457   461   463  
 467   479   487   491   499   503   509   521   523   541  
 547   557   563   569   571   577   587   593   599   601  
 607   613   617   619   631   641   643   647   653   659  
 661   673   677   683   691   701   709   719   727   733  
 739   743   751   757   761   769   773   787   797   809  
 811   821   823   827   829   839   853   857   859   863  
 877   881   883   887   907   911   919   929   937   941  
 947   953   967   971   977   983   991   997

Gambas

Click this link to run this code

'Reworked from the BBC Basic example

Public Sub Main()
Dim iNum As Integer

For iNum = 1 To 100
  If FNisprime(iNum) Then Print iNum & " is prime"
Next

End
'___________________________________________________
Public Sub FNisprime(iNum As Integer) As Boolean
Dim iLoop As Integer
Dim bReturn As Boolean = True

If iNum <= 1 Then bReturn = False
If iNum <= 3 Then bReturn = True
If (iNum And 1) = 0 Then bReturn = False

For iLoop = 3 To Sqr(iNum) Step 2
  If iNum Mod iLoop = 0 Then bReturn = False
Next

Return bReturn

End
Output:
1 is prime
3 is prime
5 is prime
7 is prime
11 is prime
......
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime

IS-BASIC

100 PROGRAM "Prime.bas"
110 FOR X=0 TO 100
120   IF PRIME(X) THEN PRINT X;
130 NEXT
140 DEF PRIME(N)
150   IF N=2 THEN
160     LET PRIME=-1
170   ELSE IF N<=1 OR MOD(N,2)=0 THEN
180     LET PRIME=0
190   ELSE
200     LET PRIME=-1
210     FOR I=3 TO CEIL(SQR(N)) STEP 2
220       IF MOD(N,I)=0 THEN LET PRIME=0:EXIT FOR
230     NEXT
240   END IF
250 END DEF

Liberty BASIC

Works with: Just BASIC
print "Rosetta Code - Primality by trial division"
print
[start]
input "Enter an integer: "; x
if x=0 then print "Program complete.": end
if isPrime(x) then print x; " is prime" else print x; " is not prime"
goto [start]

function isPrime(p)
    p=int(abs(p))
    if p=2 then isPrime=1: exit function 'prime
    if p=0 or p=1 or (p mod 2)=0 then exit function 'not prime
    for i=3 to sqr(p) step 2
        if (p mod i)=0 then exit function 'not prime
    next i
    isPrime=1
end function
Output:
Rosetta Code - Primality by trial division

Enter an integer: 1
1 is not prime
Enter an integer: 2
2 is prime
Enter an integer:
Program complete.

PureBasic

Procedure.i IsPrime(n)
   Protected k

   If n = 2
      ProcedureReturn #True
   EndIf   

   If n <= 1 Or n % 2 = 0
      ProcedureReturn #False
   EndIf
   
   For k = 3 To Int(Sqr(n)) Step 2
      If n % k = 0
         ProcedureReturn #False
      EndIf
   Next

   ProcedureReturn #True
EndProcedure

QuickBASIC

Works with: QBasic version 1.1
Works with: QuickBasic version 4.5

Returns 1 for prime, 0 for non-prime

' Primality by trial division

' Test and display primes 1 .. 50
DECLARE FUNCTION prime% (n!)
FOR n = 1 TO 50
  IF prime(n) = 1 THEN PRINT n;
NEXT n

FUNCTION prime% (n!)
  STATIC i AS INTEGER
  IF n = 2 THEN
    prime = 1
  ELSEIF n <= 1 OR n MOD 2 = 0 THEN
    prime = 0
  ELSE
    prime = 1
    FOR i = 3 TO INT(SQR(n)) STEP 2
      IF n MOD i = 0 THEN
        prime = 0
        EXIT FUNCTION
      END IF
    NEXT i
  END IF
END FUNCTION
Output:
 2  3  5  7  11  13  17  19  23  29  31  37  41  43  47

Run BASIC

Works with: Just BASIC
' Test and display primes 1 .. 50
for i = 1 TO 50
  if prime(i) <> 0 then print i;" ";
next i

FUNCTION prime(n)
if n < 2         then prime = 0 : goto [exit]
if n = 2         then prime = 1 : goto [exit]
if n mod 2 = 0   then prime = 0 : goto [exit]
prime = 1
for i = 3 to int(n^.5) step 2
 if n mod i = 0 then  prime = 0 : goto [exit]
next i
[exit]
END FUNCTION
Output:
2 3 5 7 11 13 17 19 23 25 29 31 37 41 43 47 

S-BASIC

$lines

$constant FALSE = 0
$constant TRUE = 0FFFFH

rem - return p mod q
function mod(p, q = integer) = integer
end = p - q * (p / q)

rem - return true (-1) if n is prime, otherwise false (0)
function isprime(n = integer) = integer
  var i, limit, result = integer
  if n = 2 then
    result = TRUE
  else if (n < 2) or (mod(n,2) = 0) then
    result = FALSE
  else 
    begin
      limit = int(sqr(n))
      i = 3
      while (i <= limit) and (mod(n, i) <> 0) do
        i = i + 2
      result = not (i <= limit)
    end
end = result

rem - test by looking for primes in range 1 to 50
var i = integer
for i = 1 to 50 
  if isprime(i) then print using "#####";i;
next i

end
Output:
     2    3    5    7   11   13   17   19   23   29   31   37   41   43   47

TI-83 BASIC

Prompt A
If A=2:Then
Disp "PRIME"
Stop
End

If (fPart(A/2)=0 and A>0) or A<2:Then
Disp "NOT PRIME"
Stop
End

1→P
For(B,3,int(√(A)))
If FPart(A/B)=0:Then
0→P
√(A)→B
End
B+1→B
End

If P=1:Then
Disp "PRIME"
Else
Disp "NOT PRIME"
End

Tiny BASIC

Works with: TinyBasic
10 REM Primality by trial division
20 PRINT "Enter a number "
30 INPUT P
40 GOSUB 1000
50 IF Z = 1 THEN PRINT "It is prime."
60 IF Z = 0 THEN PRINT "It is not prime."
70 END

990 REM Primality of the number P by trial division
1000 IF P < 2 THEN RETURN
1010 LET Z = 1
1020 IF P < 4 THEN RETURN
1030 LET I = 2
1040 IF (P / I) * I = P THEN LET Z = 0
1050 IF Z = 0 THEN RETURN
1060 LET I = I + 1
1070 IF I * I <= P THEN GOTO 1040
1080 RETURN

True BASIC

Translation of: QuickBASIC
FUNCTION isPrime (n)
    IF n = 2 THEN
       LET isPrime = 1
    ELSEIF n <= 1 OR REMAINDER(n, 2) = 0 THEN
       LET isPrime = 0
    ELSE
       LET isPrime = 1
       FOR i = 3 TO INT(SQR(n)) STEP 2
           IF REMAINDER(n, i) = 0 THEN
              LET isPrime = 0
              EXIT FUNCTION
           END IF
       NEXT i
    END IF
END FUNCTION

FOR n = 1 TO 50
    IF isPrime(n) = 1 THEN PRINT n;
NEXT n
END

uBasic/4tH

10 LET n=0: LET p=0
20 INPUT "Enter number: ";n
30 LET p=0 : IF n>1 THEN GOSUB 1000
40 IF p=0 THEN PRINT n;" is not prime!"
50 IF p#0 THEN PRINT n;" is prime!"
60 GOTO 10
1000 REM ***************
1001 REM * PRIME CHECK *
1002 REM ***************
1010 LET p=0
1020 IF (n%2)=0 THEN RETURN
1030 LET p=1 : PUSH n,0 : GOSUB 9030
1040 FOR i=3 TO POP() STEP 2
1050 IF (n%i)=0 THEN LET p=0: PUSH n,0 : GOSUB 9030 : LET i=POP()
1060 NEXT i
1070 RETURN
9030 Push ((10^(Pop()*2))*Pop()) : @(255)=Tos()
9040 Push (@(255) + (Tos()/@(255)))/2
     If Abs(@(255)-Tos())<2 Then @(255)=Pop() : If Pop() Then Push @(255) : Return
     @(255) = Pop() : Goto 9040
     REM ** This is an integer SQR subroutine. Output is scaled by 10^(TOS()).

VBA

Option Explicit

Sub FirstTwentyPrimes()
Dim count As Integer, i As Long, t(19) As String
   Do
      i = i + 1
      If IsPrime(i) Then
         t(count) = i
         count = count + 1
      End If
   Loop While count <= UBound(t)
   Debug.Print Join(t, ", ")
End Sub

Function IsPrime(Nb As Long) As Boolean
   If Nb = 2 Then
      IsPrime = True
   ElseIf Nb < 2 Or Nb Mod 2 = 0 Then
      Exit Function
   Else
      Dim i As Long
      For i = 3 To Sqr(Nb) Step 2
         If Nb Mod i = 0 Then Exit Function
      Next
      IsPrime = True
   End If
End Function
Output:
 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71

VBScript

Translation of: QuickBASIC
Function IsPrime(n)
	If n = 2 Then
		IsPrime = True
	ElseIf n <= 1 Or n Mod 2 = 0 Then
		IsPrime = False
	Else
		IsPrime = True
		For i = 3 To Int(Sqr(n)) Step 2
			If n Mod i = 0 Then
				IsPrime = False
				Exit For
			End If
		Next
	End If
End Function

For n = 1 To 50
	If IsPrime(n) Then
		WScript.StdOut.Write n & " "
	End If
Next
Output:
 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

Yabasic

Translation of: FreeBASIC
for i = 1 to 99
    if isPrime(i)  print str$(i), " "; 
next i
print
end

sub isPrime(v)
    if v < 2  return False
    if mod(v, 2) = 0  return v = 2
    if mod(v, 3) = 0  return v = 3
    d = 5
    while d * d <= v
        if mod(v, d) = 0 then return False else d = d + 2 : fi
    wend
    return True
end sub

ZX Spectrum Basic

10 LET n=0: LET p=0
20 INPUT "Enter number: ";n
30 IF n>1 THEN GO SUB 1000
40 IF p=0 THEN PRINT n;" is not prime!"
50 IF p<>0 THEN PRINT n;" is prime!"
60 GO TO 10
1000 REM ***************
1001 REM * PRIME CHECK *
1002 REM ***************
1010 LET p=0
1020 IF n/2=INT (n/2) THEN RETURN 
1030 LET p=1
1040 FOR i=3 TO SQR (n) STEP 2
1050 IF n/i=INT (n/i) THEN LET p=0: LET i= SQR (n) 
1060 NEXT i
1070 RETURN
Output:
15 is not prime!
17 is prime!
119 is not prime!
137 is prime!

bc

/* Return 1 if n is prime, 0 otherwise */
define p(n) {
    auto i

    if (n < 2) return(0)
    if (n == 2) return(1)
    if (n % 2 == 0) return(0)
    for (i = 3; i * i <= n; i += 2) {
        if (n % i == 0) return(0)
    }
    return(1)
}

BCPL

get "libhdr"

let sqrt(s) = 
    s <= 1 -> 1,
    valof
$(  let x0 = s >> 1
    let x1 = (x0 + s/x0) >> 1
    while x1 < x0 
    $(  x0 := x1
        x1 := (x0 + s/x0) >> 1
    $)
    resultis x0
$)

let isprime(n) =
    n < 2       -> false,
    (n & 1) = 0 -> n = 2,
    valof
$(  for i = 3 to sqrt(n) by 2
        if n rem i = 0 resultis false
    resultis true
$)

let start() be
$(  for i=1 to 100
        if isprime(i) then writef("%N ",i)
    wrch('*N')
$)
Output:
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Befunge

Reads the value to test from stdin and outputs Yes if prime and No if not.

To avoid dealing with Befunge's limited data cells, the implementation is entirely stack-based. However, this requires compressing multiple values into a single stack cell, which imposes an upper limit of 1,046,529 (10232), thus a maximum testable prime of 1,046,527.

&>:48*:**       \1`!#^_2v
v_v#`\*:%*:*84\/*:*84::+<
v >::48*:*/\48*:*%%!#v_1^
>0"seY" >:#,_@#: "No">#0<
Output:
(multiple runs)
0
No
17
Yes
49
No
97
Yes
1042441
No
1046527
Yes

Bracmat

  ( prime
  =   incs n I inc
    .   4 2 4 2 4 6 2 6:?incs
      & 2:?n
      & 1 2 2 !incs:?I
      &   whl
        ' ( !n*!n:~>!arg
          & div$(!arg.!n)*!n:~!arg
          & (!I:%?inc ?I|!incs:%?inc ?I)
          & !n+!inc:?n
          )
      & !n*!n:>!arg
  )
& 100000000000:?p
&   whl
  ' ( !p+1:<100000000100:?p
    & (   prime$!p
        & out$!p
      | 
      )
    )
& ;
Output:
100000000003
100000000019
100000000057
100000000063
100000000069
100000000073
100000000091

Brainf***

>->,[.>,]>-<++++++[-<+[---------<+]->+[->+]-<]>+<-<+[-<+]>>+[-<[->++++++++++<]>>
+]++++[->++++++++<]>.<+++++++[->++++++++++<]>+++.++++++++++.<+++++++++[->-------
--<]>--.[-]<<<->[->+>+<<]>>-[+<[[->>+>>+<<<<]>>[-<<+>>]<]>>[->-[>+>>]>[+[-<+>]>>
>]<<<<<]>[-]>[>+>]<<[-]+[-<+]->>>--]<[->+>+<<]>>>>>>>[-<<<<<->>>>>]<<<<<--[>++++
++++++[->+++++++++++<]>.+.+++++.>++++[->++++++++<]>.>]++++++++++[->+++++++++++<]
>++.++.---------.++++.--------.>++++++++++.

Explanation:

>
->,[.>,]>-<++++++[-<+[---------<+]->+[->+]-<]>+<-<+[-<+]>>+[-<[->++++++++++<]>>+]<                     takes input      
>++++[->++++++++<]>.<+++++++[->++++++++++<]>+++.++++++++++.<+++++++++[->---------<]>--.[-]<<           " is "
<->
[->+>+<<]>>-[+<[[->>+>>+<<<<]>>[-<<+>>]<]>>[->-[>+>>]>[+[-<+>]>>>]<<<<<]>[-]>[>+>]<<[-]+[-<+]->>>--]   finds # of divisors from 1 to n
<[->+>+<<]>>>>>>>[-<<<<<->>>>>]<<<<<--
[>++++++++++[->+++++++++++<]>.+.+++++.>++++[->++++++++<]>.>]                                           "not "
++++++++++[->+++++++++++<]>++.++.---------.++++.--------.>++++++++++.                                  "prime" new line

Will format as "# is/is not prime", naturally limited by cell size.

Burlesque

fcL[2==

Implicit trial division is done by the fc function. It checks if the number has exactly two divisors.

Version not using the fc function:

blsq ) 11^^2\/?dr@.%{0==}ayn!
1
blsq ) 12^^2\/?dr@.%{0==}ayn!
0
blsq ) 13^^2\/?dr@.%{0==}ayn!
1

Explanation. Given n generates a block containing 2..n-1. Calculates a block of modolus and check if it contains 0. If it contains 0 it is not a prime.

C

int is_prime(unsigned int n)
{
	unsigned int p;
	if (!(n & 1) || n < 2 ) return n == 2;

	/* comparing p*p <= n can overflow */
	for (p = 3; p <= n/p; p += 2)
		if (!(n % p)) return 0;
	return 1;
}

C#

static bool isPrime(int n)
        {
            if (n <= 1) return false;
            for (int i = 2; i * i <= n; i++)            
                if (n % i == 0) return false;            
            return true;
        }

C++

#include <cmath>

bool is_prime(unsigned int n)
{
    if (n <= 1)
        return false;
    if (n == 2)
        return true;
    for (unsigned int i = 2; i <= sqrt(n); ++i)
        if (n % i == 0)
            return false;
    return true;
}

Chapel

Translation of: C++
proc is_prime(n)
{
    if n == 2 then
        return true;
    if n <= 1 || n % 2 == 0 then
        return false;
    for i in 3..floor(sqrt(n)):int by 2 do
        if n % i == 0 then
            return false;
    return true;
}

Clojure

The function used in both versions:

(defn divides? [k n] (zero? (mod k n)))

Testing divisors are in range from 3 to  n    with step 2:

(defn prime? [x]
  (or (= 2 x)
      (and (< 1 x)
           (odd? x)
           (not-any? (partial divides? x)
                     (range 3 (inc (Math/sqrt x)) 2)))))

Testing only prime divisors:

(declare prime?)

(def primes (filter prime? (range)))

(defn prime? [x]
  (and (integer? x)
       (< 1 x)
       (not-any? (partial divides? x)
                 (take-while (partial >= (Math/sqrt x)) primes))))

CLU

isqrt = proc (s: int) returns (int)
    x0: int := s/2
    if x0=0 then return(s) end
    x1: int := (x0 + s/x0)/2
    while x1 < x0 do
        x0 := x1
        x1 := (x0 + s/x0)/2
    end
    return(x0)
end isqrt

prime = proc (n: int) returns (bool)
    if n<=2 then return(n=2) end
    if n//2=0 then return(false) end
    for d: int in int$from_to_by(3,isqrt(n),2) do
        if n//d=0 then return(false) end
    end
    return(true)
end prime

start_up = proc ()
    po: stream := stream$primary_input()
    for i: int in int$from_to(1,100) do
        if prime(i) then
            stream$puts(po, int$unparse(i) || " ")
        end
    end
end start_up
Output:
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

CMake

# Prime predicate: does n be a prime number? Sets var to true or false.
function(primep var n)
  if(n GREATER 2)
    math(EXPR odd "${n} % 2")
    if(odd)
      # n > 2 and n is odd.
      set(factor 3)
      # Loop for odd factors from 3, while factor <= n / factor.
      math(EXPR quot "${n} / ${factor}")
      while(NOT factor GREATER quot)
        math(EXPR rp "${n} % ${factor}")        # Trial division
        if(NOT rp)
          # factor divides n, so n is not prime.
          set(${var} false PARENT_SCOPE)
          return()
        endif()
        math(EXPR factor "${factor} + 2")       # Next odd factor
        math(EXPR quot "${n} / ${factor}")
      endwhile(NOT factor GREATER quot)
      # Loop found no factor, so n is prime.
      set(${var} true PARENT_SCOPE)
    else()
      # n > 2 and n is even, so n is not prime.
      set(${var} false PARENT_SCOPE)
    endif(odd)
  elseif(n EQUAL 2)
    set(${var} true PARENT_SCOPE)       # 2 is prime.
  else()
    set(${var} false PARENT_SCOPE)      # n < 2 is not prime.
  endif()
endfunction(primep)
# Quick example.
foreach(i -5 1 2 3 37 39)
  primep(b ${i})
  if(b)
    message(STATUS "${i} is prime.")
  else()
    message(STATUS "${i} is _not_ prime.")
  endif(b)
endforeach(i)

COBOL

       Identification Division.
       Program-Id. Primality-By-Subdiv.

       Data Division.
       Working-Storage Section.
       78  True-Val  Value 0.
       78  False-Val Value 1.

       Local-Storage Section.
       01  lim Pic 9(10).
       01  i   Pic 9(10).

       Linkage Section.
       01  num    Pic 9(10).
       01  result Pic 9.

       Procedure Division Using num result.
       Main.
           If num <= 1
               Move False-Val To result
               Goback
           Else If num = 2
               Move True-Val To result
               Goback
           End-If

           Compute lim = Function Sqrt(num) + 1
           Perform Varying i From 3 By 1 Until lim < i
               If Function Mod(num, i) = 0
                   Move False-Val To result
                   Goback
               End-If
           End-Perform

           Move True-Val To Result

           Goback
           .

CoffeeScript

is_prime = (n) ->
  # simple prime detection using trial division, works
  # for all integers
  return false if n <= 1 # by definition
  p = 2
  while p * p <= n
    return false if n % p == 0
    p += 1
  true
  
for i in [-1..100]
  console.log i if is_prime i

Common Lisp

(defun primep (n)
  "Is N prime?"
  (and (> n 1) 
       (or (= n 2) (oddp n))
       (loop for i from 3 to (isqrt n) by 2
	  never (zerop (rem n i)))))

Alternate solution

I use Allegro CL 10.1

;; Project : Primality by trial division

(defun prime(n)
         (setq flag 0)
         (loop for i from 2 to (- n 1) do
                 (if (= (mod n i) 0)
                     (setq flag 1)))
                 (if (= flag 0)
                     (format t "~d is a prime number" n)
                     (format t "~d is not a prime number" n)))
(prime 7)
(prime 8)

Output:

7 is a prime number
8 is not a prime number

Cowgol

include "cowgol.coh";

sub prime(n: uint32): (isprime: uint8) is
    isprime := 1;

    if n < 2 then
        isprime := 0;
        return;
    end if;

    if n & 1 == 0 then
        if n != 2 then
            isprime := 0;
        end if;
        return;
    end if;

    var factor: uint32 := 3;
    while factor * factor <= n loop
        if n % factor == 0 then
            isprime := 0;
            return;
        end if;
        factor := factor + 2;
    end loop;
end sub;

var i: uint32 := 0;
while i <= 100 loop
    if prime(i) != 0 then
        print_i32(i);
        print_nl();
    end if;
    i := i + 1;
end loop;
Output:
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97

Crystal

Mathematicaly basis of Prime Generators
https://www.academia.edu/19786419/PRIMES-UTILS_HANDBOOK 
https://www.academia.edu/42734410/Improved_Primality_Testing_and_Factorization_in_Ruby_revised
require "big"
require "benchmark"

# the simplest PG primality test using the P3 prime generator
# reduces the number space for primes to 2/6 (33.33%) of all integers

def primep3?(n)                           # P3 Prime Generator primality test
  # P3 = 6*k + {5, 7}                     # P3 primes candidates (pc) sequence
  n = n.to_big_i
  return n | 1 == 3 if n < 5              # n: 0,1,4|false, 2,3|true 
  return false if n.gcd(6) != 1           # 1/3 (2/6) of integers are P3 pc
  p = typeof(n).new(5)                    # first P3 sequence value
  until p > isqrt(n)
    return false if n % p == 0 || n % (p + 2) == 0  # if n is composite
    p += 6      # first prime candidate for next kth residues group
  end
  true
end

# PG primality test using the P5 prime generator
# reduces the number space for primes to 8/30 (26.67%) of all integers

def primep5?(n)                          # P5 Prime Generator primality test
  # P5 = 30*k + {7,11,13,17,19,23,29,31} # P5 primes candidates sequence
  n = n.to_big_i
  return [2, 3, 5].includes?(n) if n < 7 # for small and negative values
  return false if n.gcd(30) != 1         # 4/15 (8/30) of integers are P5 pc
  p = typeof(n).new(7)                   # first P5 sequence value
  until p > isqrt(n)
    return false if                      # if n is composite
      n % (p)    == 0 || n % (p+4)  == 0 || n % (p+6)  == 0 || n % (p+10) == 0 ||
      n % (p+12) == 0 || n % (p+16) == 0 || n % (p+22) == 0 || n % (p+24) == 0
      p += 30  # first prime candidate for next kth residues group
  end
  true
end

# PG primality test using the P7 prime generator
# reduces the number space for primes to 48/210 (22.86%) of all integers

def primep7?(n)
  # P7 = 210*k + {11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,
  #      89,97,101,103,107,109,113,121,127,131,137,139,143,149,151,157,163,
  #      167,169,173,179,181,187,191,193,197,199,209,211}
  n = n.to_big_i
  return [2, 3, 5, 7].includes?(n) if n < 11  
  return false if n.gcd(210) != 1         # 8/35 (48/210) of integers are P7 pc
  p = typeof(n).new(11)                   # first P7 sequence value
  until p > isqrt(n)
    return false if
      n % (p)     == 0 || n % (p+2)   == 0 || n % (p+6)   == 0 || n % (p+8)   == 0 ||
      n % (p+12)  == 0 || n % (p+18)  == 0 || n % (p+20)  == 0 || n % (p+26)  == 0 ||
      n % (p+30)  == 0 || n % (p+32)  == 0 || n % (p+36)  == 0 || n % (p+42)  == 0 ||
      n % (p+48)  == 0 || n % (p+50)  == 0 || n % (p+56)  == 0 || n % (p+60)  == 0 ||
      n % (p+62)  == 0 || n % (p+68)  == 0 || n % (p+72)  == 0 || n % (p+78)  == 0 ||
      n % (p+86)  == 0 || n % (p+90)  == 0 || n % (p+92)  == 0 || n % (p+96)  == 0 ||
      n % (p+98)  == 0 || n % (p+102) == 0 || n % (p+110) == 0 || n % (p+116) == 0 ||
      n % (p+120) == 0 || n % (p+126) == 0 || n % (p+128) == 0 || n % (p+132) == 0 ||
      n % (p+138) == 0 || n % (p+140) == 0 || n % (p+146) == 0 || n % (p+152) == 0 ||
      n % (p+156) == 0 || n % (p+158) == 0 || n % (p+162) == 0 || n % (p+168) == 0 ||
      n % (p+170) == 0 || n % (p+176) == 0 || n % (p+180) == 0 || n % (p+182) == 0 ||
      n % (p+186) == 0 || n % (p+188) == 0 || n % (p+198) == 0 || n % (p+200) == 0
    p += 210    # first prime candidate for next  kth residues group 
  end
  true
end

# Newton's method for integer squareroot
def isqrt(n)
  raise ArgumentError.new "Input must be non-negative integer" if n < 0
  return n if n < 2
  bits = n.bit_length
  one = typeof(n).new(1)  # value 1 of type self
  x = one << ((bits - 1) >> 1) | n >> ((bits >> 1) + 1)
  while (t = n // x) < x; x = (x + t) >> 1 end
  x   # output is same integer class as input
end

# Benchmarks to test for various size primes

p = 541
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    puts
end

p = 1000003      
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    puts
end

p = 2147483647i32     # largest I32 prime
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    puts
end

p = 4294967291u32     # largest U32 prime
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    puts
end

p = 4294967311      # first prime > 2**32
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    puts
end
Output:
p = 541
primep3? 290.17k (  3.45µs) (± 2.76%)  1.35kB/op   1.64× slower
primep5? 476.47k (  2.10µs) (± 1.75%)    802B/op        fastest
primep7? 128.44k (  7.79µs) (± 2.82%)  2.66kB/op   3.71× slower

p = 1000003
primep3?  11.24k ( 88.97µs) (± 2.34%)  33.9kB/op   2.48× slower
primep5?  21.91k ( 45.64µs) (± 2.88%)  16.6kB/op   1.27× slower
primep7?  27.83k ( 35.94µs) (± 2.68%)  11.9kB/op        fastest

p = 2147483647
primep3? 105.11  (  9.51ms) (± 3.25%)  3.89MB/op   5.56× slower
primep5? 317.49  (  3.15ms) (± 2.40%)   1.2MB/op   1.84× slower
primep7? 584.92  (  1.71ms) (± 3.09%)   591kB/op        fastest

p = 4294967291
primep3? 168.56  (  5.93ms) (± 2.39%)  2.17MB/op   2.69× slower
primep5? 349.24  (  2.86ms) (± 2.86%)  1.03MB/op   1.30× slower
primep7? 454.08  (  2.20ms) (± 2.62%)   739kB/op        fastest

p = 4294967311
primep3?  84.61  ( 11.82ms) (± 2.35%)  4.68MB/op   5.02× slower
primep5? 248.62  (  4.02ms) (± 2.21%)  1.54MB/op   1.71× slower
primep7? 424.61  (  2.36ms) (± 2.73%)   813kB/op        fastest

D

Simple Version

import std.stdio, std.algorithm, std.range, std.math;

bool isPrime1(T)(in T n) pure nothrow {
	if (n == 2)
        return true;
	
    if (n <= 1 || (n & 1) == 0)
        return false;
	
    for(T i = 3; i <= real(n).sqrt; i += 2)
        if (n % i == 0)
            return false;
	
    return true;
}


void main() {
    iota(2, 40).filter!isPrime1.writeln;
}
Output:
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]

Version with excluded multiplies of 2 and 3

Same output.

bool isPrime2(It)(in It n) pure nothrow {
    // Adapted from: http://www.devx.com/vb2themax/Tip/19051
    // Test 1, 2, 3 and multiples of 2 and 3:
    if (n == 2 || n == 3)
        return true;
    else if (n < 2 || n % 2 == 0 || n % 3 == 0)
        return false;

    // We can now avoid to consider multiples of 2 and 3. This
    // can be done really simply by starting at 5 and
    // incrementing by 2 and 4 alternatively, that is:
    //   5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 35, 37, ...
    // We don't need to go higher than the square root of the n.
    for (It div = 5, inc = 2; div ^^ 2 <= n; div += inc, inc = 6 - inc)
        if (n % div == 0)
            return false;

    return true;
}

void main() {
    import std.stdio, std.algorithm, std.range;

    iota(2, 40).filter!isPrime2.writeln;
}

Two Way Test

Odd divisors is generated both from increasing and decreasing sequence, may improve performance for numbers that have large minimum factor. Same output.

import std.stdio, std.algorithm, std.range, std.math;

bool isPrime3(T)(in T n) pure nothrow {
    if (n % 2 == 0 || n <= 1)
        return n == 2;
    T head = 3, tail = (cast(T)real(n).sqrt / 2) * 2 + 1;
    for ( ; head <= tail ; head +=2, tail -= 2)
        if ((n % head) == 0 || (n % tail) == 0)
            return false;
    return true;
}

void main() {
    iota(2, 40).filter!isPrime3.writeln;
}

Dart

import 'dart:math';

bool isPrime(int n) {
  if (n <= 1) return false;
  if (n == 2) return true;
  for (int i = 2; i <= sqrt(n); ++i) if (n % i == 0) return false;
  return true;
}

void main() {
  for (int i = 1; i <= 99; ++i) if (isPrime(i)) print('$i ');
}

Delphi

First

function IsPrime(aNumber: Integer): Boolean;
var
  I: Integer;
begin
  Result:= True;
  if(aNumber = 2) then Exit;

  Result:= not ((aNumber mod 2 = 0)  or
                (aNumber <= 1));
  if not Result then Exit;

  for I:=3 to Trunc(Sqrt(aNumber)) do
  if(aNumber mod I = 0) then
  begin
    Result:= False;
    Break;
  end;
end;

Second

function IsPrime(const x: integer): Boolean;
var
  i: integer;
begin
  i := 2;
  repeat
    if X mod i = 0 then
    begin
      Result := False;
      Exit;
    end;
    Inc(i);
  until i > Sqrt(x);
  Result := True;
end;

Draco

proc prime(word n) bool:
    word factor;
    bool composite;
    if n<=4 then
        n=2 or n=3
    elif n&1 = 0 then
        false
    else
        factor := 3;
        composite := false;
        while not composite and factor*factor <= n do
            composite := n % factor = 0;
            factor := factor + 2
        od;
        not composite
    fi
corp

proc main() void:
    word i;
    for i from 0 upto 100 do
        if prime(i) then
            writeln(i)
        fi
    od
corp
Output:
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97

E

Translation of: D
def isPrime(n :int) {
    if (n == 2) {
        return true
    } else if (n <= 1 || n %% 2 == 0) {
        return false
    } else {
        def limit := (n :float64).sqrt().ceil()
        var divisor := 1
        while ((divisor += 2) <= limit) {
            if (n %% divisor == 0) {
                return false
            }
        }
        return true
    }
}

EasyLang

func isprim n .
   if n < 2
      return 0
   .
   if n mod 2 = 0 and n > 2
      return 0
   .
   i = 3
   sq = sqrt n
   while i <= sq
      if n mod i = 0
         return 0
      .
      i += 2
   .
   return 1
.
print isprim 1995937

EchoLisp

(lib 'sequences)

;; Try divisors iff n = 2k + 1
(define (is-prime? p)
	(cond
	[(< p 2) #f]
	[(zero? (modulo p 2)) (= p 2)]
	[else 
	(for/and ((d [3 5 .. (1+ (sqrt p))] ))  (!zero? (modulo p d)))]))

(filter is-prime? (range 1 100))
     (2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97)

;; Improve performance , try divisors iff  n = 6k+1 or n = 6k+5
(define (is-prime? p)
	(cond
	[(< p 2) #f]
	[(zero? (modulo p 2)) (= p 2)]
	[(zero? (modulo p 3)) (= p 3)]
	[(zero? (modulo p 5)) (= p 5)]
	[else  ;; step 6 : try divisors 6n+1 or 6n+5
		(for ((d [7 13 .. (1+ (sqrt p))] ))  
			#:break (zero? (modulo p d)) => #f
			#:break (zero? (modulo p (+ d 4))) => #f
			#t )]))
	
(filter is-prime? (range 1 100))
     (2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97)

Eiffel

class
	APPLICATION

create
	make

feature

	make
                -- Tests the feature is_prime.
		do
			io.put_boolean (is_prime (1))
			io.new_line
			io.put_boolean (is_prime (2))
			io.new_line
			io.put_boolean (is_prime (3))
			io.new_line
			io.put_boolean (is_prime (4))
			io.new_line
			io.put_boolean (is_prime (97))
			io.new_line
			io.put_boolean (is_prime (15589))
			io.new_line
		end

	is_prime (n: INTEGER): BOOLEAN
                -- Is 'n' a prime number?
		require
			positiv_input: n > 0
		local
			i: INTEGER
			max: REAL_64
			math: DOUBLE_MATH
		do
			create math
			if n = 2 then
				Result := True
			elseif n <= 1 or n \\ 2 = 0 then
				Result := False
			else
				Result := True
				max := math.sqrt (n)
				from
					i := 3
				until
					i > max
				loop
					if n \\ i = 0 then
						Result := False
					end
					i := i + 2
				end
			end
		end

end
False
True
True
False
True
False

Elixir

Translation of: Erlang
defmodule RC do
  def is_prime(2), do: true
  def is_prime(n) when n<2 or rem(n,2)==0, do: false
  def is_prime(n), do: is_prime(n,3)
  
  def is_prime(n,k) when n<k*k, do: true
  def is_prime(n,k) when rem(n,k)==0, do: false
  def is_prime(n,k), do: is_prime(n,k+2)
end

IO.inspect for n <- 1..50, RC.is_prime(n), do: n
Output:
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

Emacs Lisp

Library: cl-lib
(defun prime (a)
  (not (or (< a 2)
           (cl-loop for x from 2 to (sqrt a)
                    when (zerop (% a x))
                    return t))))

More concise, a little bit faster:

(defun prime2 (a)
  (and (> a 1)
       (cl-loop for x from 2 to (sqrt a)
                never (zerop (% a x)))))

A little bit faster:

(defun prime3 (a)
  (and (> a 1)
       (or (= a 2) (cl-oddp a))
       (cl-loop for x from 3 to (sqrt a) by 2
                never (zerop (% a x)))))

More than 2 times faster, than the previous, doesn't use loop macro:

(defun prime4 (a)
  (not (or (< a 2)
           (cl-some (lambda (x) (zerop (% a x))) (number-sequence 2 (sqrt a))))))

Almost 2 times faster, than the previous:

(defun prime5 (a)
  (not (or (< a 2)
           (and (/= a 2) (cl-evenp a))
           (cl-some (lambda (x) (zerop (% a x))) (number-sequence 3 (sqrt a) 2)))))

Erlang

is_prime(N) when N == 2 -> true;
is_prime(N) when N < 2 orelse N rem 2 == 0 -> false;
is_prime(N) -> is_prime(N,3).

is_prime(N,K) when K*K > N -> true;
is_prime(N,K) when N rem K == 0 -> false;
is_prime(N,K) -> is_prime(N,K+2).

ERRE

PROGRAM PRIME_TRIAL

PROCEDURE ISPRIME(N%->OK%)
      LOCAL T%
      IF N%<=1 THEN OK%=FALSE  EXIT PROCEDURE END IF
      IF N%<=3 THEN OK%=TRUE EXIT PROCEDURE END IF
      IF (N% AND 1)=0 THEN OK%=FALSE EXIT PROCEDURE END IF
      FOR T%=3 TO SQR(N%) STEP 2 DO
        IF N% MOD T%=0 THEN OK%=FALSE EXIT PROCEDURE END IF
      END FOR
      OK%=TRUE
END PROCEDURE

BEGIN

      FOR I%=1 TO 100 DO
         ISPRIME(I%->OK%)
         IF OK% THEN PRINT(i%;"is prime") END IF
      END FOR

END PROGRAM
Output:
2 is prime
3 is prime
5 is prime
7  is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime

Euphoria

function is_prime(integer n)
    if n<=2 or remainder(n,2)=0 then
        return 0
    else
        for i=3 to sqrt(n) by 2 do
            if remainder(n,i)=0 then
                return 0
            end if
        end for
        return 1
    end if
end function

F#

open NUnit.Framework
open FsUnit
let inline isPrime n = not ({uint64 2..uint64 (sqrt (double n))} |> Seq.exists (fun (i:uint64) -> uint64 n % i = uint64 0))
[<Test>]
let ``Validate that 2 is prime`` () =
  isPrime 2 |> should equal true
 
[<Test>]
let ``Validate that 4 is not prime`` () =
  isPrime 4 |> should equal false
 
[<Test>]
let ``Validate that 3 is prime`` () =
  isPrime 3 |> should equal true
 
[<Test>]
let ``Validate that 9 is not prime`` () =
  isPrime 9 |> should equal false
 
[<Test>]
let ``Validate that 5 is prime`` () =
  isPrime 5 |> should equal true
 
[<Test>]
let ``Validate that 277 is prime`` () =
  isPrime 277 |> should equal true
Output:
> isPrime 1111111111111111111UL;;
val it : bool = true

and if you want to test really big numbers, use System.Numerics.BigInteger, but it's slower:

let isPrimeI x =
    if x < 2I then false else
    if x = 2I then true else
    if x % 2I = 0I then false else
    let rec test n =
      if n * n > x then true else
      if x % n = 0I then false else test (n + 2I) in test 3I

If you have a lot of prime numbers to test, caching a sequence of primes can speed things up considerably, so you only have to do the divisions against prime numbers.

let rec primes = Seq.cache(Seq.append (seq[ 2; 3; 5 ]) (Seq.unfold (fun state -> Some(state, state + 2)) 7 |> Seq.filter (fun x -> IsPrime x)))
    
and IsPrime number =
    let rec IsPrimeCore number current limit =
        let cprime = primes |> Seq.nth current
        if cprime >= limit then
            true
        else if number % cprime = 0 then
            false
        else
            IsPrimeCore number (current + 1) (number/cprime)

    if number = 2 then
        true
    else if number < 2 then
        false
    else
        IsPrimeCore number 0 number

Factor

USING: combinators kernel math math.functions math.ranges sequences ;

: prime? ( n -- ? )
    {
        { [ dup 2 < ] [ drop f ] }
        { [ dup even? ] [ 2 = ] }
        [ 3 over sqrt 2 <range> [ mod 0 > ] with all? ]
    } cond ;

FALSE

[0\$2=$[@~@@]?~[$$2>\1&&[\~\
   3[\$@$@1+\$*>][\$@$@$@$@\/*=[%\~\$]?2+]#%
]?]?%]p:


Forth

: prime? ( n -- f )
        dup 2 < if      drop false
    else dup 2 = if      drop true
    else dup 1 and 0= if drop false
    else 3
        begin 2dup dup * >=
        while 2dup mod 0=
              if       2drop false exit
              then 2 +
        repeat         2drop true
    then then then ;

Fortran

Works with: Fortran version 90 and later
 FUNCTION isPrime(number)
   LOGICAL :: isPrime
   INTEGER, INTENT(IN) :: number
   INTEGER :: i
 
   IF(number==2) THEN
      isPrime = .TRUE.
   ELSE IF(number < 2 .OR. MOD(number,2) == 0) THEN
      isPRIME = .FALSE.
   ELSE
      isPrime = .TRUE.
      DO i = 3, INT(SQRT(REAL(number))), 2
         IF(MOD(number,i) == 0) THEN
            isPrime = .FALSE.
            EXIT
         END IF
      END DO
   END IF
 END FUNCTION

Frink

It is unnecessary to write this function because Frink has an efficient isPrime[x] function to test primality of arbitrarily-large integers. Here is a version that works for arbitrarily-large integers. Beware some of these solutions that calculate up to sqrt[x] but because of floating-point error the square root is slightly smaller than the true square root!

isPrimeByTrialDivision[x] :=
{
   for p = primes[]
   {
      if p*p > x
         return true
      if x mod p == 0
         return false
   }
      
   return true     
}

FunL

import math.sqrt

def
  isPrime( 2 )      =  true
  isPrime( n )
    | n < 3 or 2|n  =  false
    | otherwise     =  (3..int(sqrt(n)) by 2).forall( (/|n) )

(10^10..10^10+50).filter( isPrime ).foreach( println )
Output:
10000000019
10000000033


GAP

IsPrimeTrial := function(n)
   local k, m;
   if n < 5 then
      return (n = 2) or (n = 3);
   fi;
   if RemInt(n, 2) = 0 then
      return false;
   fi;
   m := RootInt(n);
   k := 3;
   while k <= m do
      if RemInt(n, k) = 0 then
         return false;
      fi;
      k := k + 2;
   od;
   return true;
end;

Filtered([1 .. 100], IsPrimeTrial);                              
# [ 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97 ]

Go

func IsPrime(n int) bool {
	if n < 0 { n = -n }
	switch {
        case n == 2:
		return true
	case n < 2 || n % 2 == 0:
		return false
	
	default:
		for i = 3; i*i <= n; i += 2 {
			if n % i == 0 { return false }
		}
	}
	return true
}

Or, using recursion:

func IsPrime(n int) bool {
	if n < 0 { n = -n }
	if n <= 2 { 
		return n == 2 
	}
	return n % 2 != 0 && isPrime_r(n, 3)
}

func isPrime_r(n, i int) bool {
	if i*i <= n {
		return n % i != 0 && isPrime_r(n, i+2)
	}
	return true
}

Groovy

def isPrime = {
    it == 2 || 
    it > 1 &&
    (2..Math.max(2, (int) Math.sqrt(it))).every{ k -> it % k != 0 }
}

(0..20).grep(isPrime)
Output:
[2, 3, 5, 7, 11, 13, 17, 19]

Haskell

(used here and here). The basic divisibility test by odd numbers:

isPrime n = n==2 || n>2 && all ((> 0).rem n) (2:[3,5..floor.sqrt.fromIntegral $ n+1])

Testing by prime numbers only is faster. Primes list is saved for reuse. Precalculation of primes pays off if testing more than just a few numbers, and/or primes are generated efficiently enough:

noDivsBy factors n = foldr (\f r-> f*f>n || ((rem n f /= 0) && r)) True factors 

-- primeNums = filter (noDivsBy [2..]) [2..]
--           = 2 : filter (noDivsBy [3,5..]) [3,5..] 
primeNums = 2 : 3 : filter (noDivsBy $ tail primeNums) [5,7..]

isPrime n = n > 1 && noDivsBy primeNums n

Any increasing unbounded sequence of numbers that includes all primes (above the first few, perhaps) could be used with the testing function noDivsBy to define the isPrime function -- but using just primes is better, produced e.g. by Sieve of Eratosthenes, or noDivsBy itself can be used to define primeNums as shown above, because it stops when the square root is reached (so there's no infinite recursion, no "vicious circle").

A less efficient, more basic variant:

isPrime n = n > 1 && []==[i | i <- [2..n-1], rem n i == 0]

The following is an attempt at improving it, resulting in absolutely worst performing prime testing code I've ever seen, ever. A curious oddity.

isPrime n = n > 1 && []==[i | i <- [2..n-1], isPrime i && rem n i == 0]

HicEst

   DO n = 1, 1E6
     Euler = n^2 + n + 41
     IF( Prime(Euler) == 0 ) WRITE(Messagebox) Euler, ' is NOT prime for n =', n
   ENDDO                            ! e.g.    1681 = 40^2 + 40 + 41 is NOT prime
END

FUNCTION Prime(number)
   Prime = number == 2
   IF( (number > 2) * MOD(number,2) ) THEN
     DO i = 3, number^0.5, 2
       IF(MOD(number,i) == 0) THEN
         Prime = 0
         RETURN
       ENDIF
     ENDDO
     Prime = 1
   ENDIF
END

Icon and Unicon

Procedure shown without a main program.

procedure isprime(n)                            #: return n if prime (using trial division) or fail
if not n = integer(n) | n < 2 then fail         # ensure n is an integer greater than 1
every if 0 = (n % (2 to sqrt(n))) then fail
return n
end

J

Generally, this task should be accomplished in J using 1&p:. Here we take an approach that's more comparable with the other examples on this page.
isprime=: 3 : 'if. 3>:y do. 1<y else. 0 *./@:< y|~2+i.<.%:y end.'

Java

public static boolean prime(long a){
   if(a == 2){
      return true;
   }else if(a <= 1 || a % 2 == 0){
      return false;
   }
   long max = (long)Math.sqrt(a);
   for(long n= 3; n <= max; n+= 2){
      if(a % n == 0){ return false; }
   }
   return true;
}

By Regular Expression

public static boolean prime(int n) {
    return !new String(new char[n]).matches(".?|(..+?)\\1+");
}

JavaScript

function isPrime(n) {
  if (n == 2 || n == 3 || n == 5 || n == 7) {
    return true;
  } else if ((n < 2) || (n % 2 == 0)) {
    return false;
  } else {
    for (var i = 3; i <= Math.sqrt(n); i += 2) {
      if (n % i == 0)
        return false;
    }
    return true;
  }
}

Joy

DEFINE prime ==
2 [[dup * >] nullary [rem 0 >] dip and]
[succ] while dup * <.

jq

def is_prime:

  if . == 2 then true
  else 2 < . and . % 2 == 1 and
       . as $in
       | (($in + 1) | sqrt) as $m
       | (((($m - 1) / 2) | floor) + 1) as $max
       | all( range(1; $max) ; $in % ((2 * .) + 1) > 0 )
  end;

Example -- the command line is followed by alternating lines of input and output: $ jq -f is_prime.jq

-2
false
1
false
2
true
100
false

Note: if your jq does not have all, the following will suffice:

def all(generator; condition):
  reduce generator as $i (true; . and ($i|condition));

Julia

Julia already has an isprime function, so this function has the verbose name isprime_trialdivision to avoid overriding the built-in function. Note this function relies on the fact that Julia skips for-loops having invalid ranges. Otherwise the function would have to include additional logic to check the odd numbers less than 9.

function isprime_trialdivision{T<:Integer}(n::T)
    1 < n || return false
    n != 2 || return true
    isodd(n) || return false
    for i in 3:isqrt(n)
        n%i != 0 || return false
    end
    return true
end

n = 100
a = filter(isprime_trialdivision, [1:n])

if all(a .== primes(n))
    println("The primes <= ", n, " are:\n    ", a)
else
    println("The function does not accurately calculate primes.")
end
Output:
The primes <= 100 are:
   [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97]

K

   isprime:{(x>1)&&/x!'2_!1+_sqrt x}
   &isprime'!100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Kotlin

// version 1.1.2
fun isPrime(n: Int): Boolean {
    if (n < 2) return false
    if (n % 2 == 0) return n == 2
    val limit = Math.sqrt(n.toDouble()).toInt()
    return (3..limit step 2).none { n % it == 0 }
}

fun main(args: Array<String>) {
    // test by printing all primes below 100 say
    (2..99).filter { isPrime(it) }.forEach { print("$it ") }
}
Output:
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Lambdatalk

1) the simplest

{def isprime1
 {def isprime1.loop
  {lambda {:n :m :i}
   {if {> :i :m}
    then true
    else {if {= {% :n :i} 0}
    then false
    else {isprime1.loop :n :m {+ :i 1}} }
 }}}
 {lambda {:n}
  {isprime1.loop :n {sqrt :n} 2} 
}}
-> isprime1

2) slightly improved

{def isprime2
 {def isprime2.loop
  {lambda {:n :m :i}
   {if {> :i :m}
    then true
    else {if {= {% :n :i} 0}
    then false
    else {isprime2.loop :n :m {+ :i 2}}
 }}}}
 {lambda {:n}
  {if {or {= :n 2} {= :n 3} {= :n 5} {= :n 7}}
   then true
   else {if {or {< : n 2} {= {% :n 2} 0}}
   then false
   else {isprime2.loop :n {sqrt :n} 3} 
}}}}
-> isprime2

3) testing

{isprime1 1299709} -> stackoverflow on my iPad Pro
{isprime2 1299709} -> true

{def primesTo
 {lambda {:f :n}
  {S.replace \s by space in 
   {S.map {{lambda {:f :i} {if {:f :i} then :i else}} :f}
          {S.serie 2 :n}}} }}
-> primesTo

{primesTo isprime1 100}
-> 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97  in 25ms
{primesTo isprime2 100}
-> 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97  in 20ms

{primesTo isprime1 1000000}  in about 30000ms
{primesTo isprime2 1000000}  in about 15000ms

langur

Recursive

Translation of: Go
Works with: langur version 0.11
val .isPrime = f(.i) {
    val .n = abs(.i)
    if .n <= 2: return .n == 2

    val .chkdiv = f(.n, .i) {
        if .i x .i <= .n {
            return .n ndiv .i and self(.n, .i+2)
        }
        return true
    }

    return .n ndiv 2 and .chkdiv(.n, 3)
}

writeln filter .isPrime, series 100

Functional

Translation of: Raku

following the Raku example, which states, "Integer $i is prime if it is greater than one and is divisible by none of 2, 3, up to the square root of $i" (plus an adjustment for the prime number 2)

Below, we use an implied parameter (.i) on the .isPrime function.

Works with: langur version 0.11
val .isPrime = f .i == 2 or
    .i > 2 and not any f(.x) .i div .x, pseries 2 .. .i ^/ 2

writeln filter .isPrime, series 100
Output:
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

Lingo

on isPrime (n)
    if n<=1 or (n>2 and n mod 2=0) then return FALSE
    sq = sqrt(n)
    repeat with i = 3 to sq
        if n mod i = 0 then return FALSE
    end repeat
    return TRUE
end
primes = []
repeat with i = 0 to 100
    if isPrime(i) then primes.add(i)
end repeat
put primes
Output:
-- [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

to prime? :n
   if :n < 2 [output "false]
   if :n = 2 [output "true]
   if equal? 0 modulo :n 2 [output "false]
   for [i 3 [sqrt :n] 2] [if equal? 0 modulo :n :i [output "false]]
   output "true
end

LSE64

over : 2 pick
 2dup : over over
 even? : 1 & 0 =
 
 # trial n d yields "n d 0/1 false" or "n d+2 true"
 trial : 2 +                 true
 trial : 2dup % 0 =   then 0 false
 trial : 2dup dup * < then 1 false
 trial-loop : trial &repeat
 
 # prime? n yields flag
 prime? : 3 trial-loop >flag drop drop
 prime? : dup even? then drop false
 prime? : dup 2 =   then drop true
 prime? : dup 2 <   then drop false

Lua

function IsPrime( n )
    if n <= 1 or ( n ~= 2 and n % 2 == 0 ) then
        return false
    end

    for i = 3, math.sqrt(n), 2 do
	if n % i == 0 then
  	    return false
	end
    end

    return true
end

Type of number Decimal.

M2000 Interpreter

Module Primality_by_trial_division {
	Inventory Known1=2@, 3@
	IsPrime=lambda  Known1 (x as decimal) -> {
		=false
		if exist(Known1, x) then =true : exit
		if x<=5 OR frac(x) then {if x == 2 OR x == 3 OR x == 5 then Append Known1, x  : =true
		Break}
		if frac(x/2) else exit
		if frac(x/3) else exit
		x1=sqrt(x):d = 5@	      	
		do
			if frac(x/d) else exit
			d += 2: if d>x1 then Append Known1, x : =true : exit
			if frac(x/d) else exit
			d += 4: if d<= x1 else Append Known1, x :  =true: exit
		always
	}
	
	i=2
	While Len(Known1)<20 
		dummy=Isprime(i)        
		i++
	End While
	Print "first ";len(known1);" primes"
	Print Known1
	Print "From 110 to 130"
	count=0
	For i=110 to 130
		If isPrime(i) Then Print i, : count++
	Next
	Print
	Print "Found ";count;" primes"
}
Primality_by_trial_division

M4

define(`testnext',
   `ifelse(eval($2*$2>$1),1,
      1,
      `ifelse(eval($1%$2==0),1,
         0,
         `testnext($1,eval($2+2))')')')
define(`isprime',
   `ifelse($1,2,
      1,
      `ifelse(eval($1<=1 || $1%2==0),1,
         0,
         `testnext($1,3)')')')

isprime(9)
isprime(11)
Output:
0
1

MAD

            NORMAL MODE IS INTEGER

            INTERNAL FUNCTION(N)
            ENTRY TO PRIME.
            WHENEVER N.L.2, FUNCTION RETURN 0B
            WHENEVER N.E.N/2*2, FUNCTION RETURN N.E.2
            THROUGH TRIAL, FOR FAC=3, 2, FAC*FAC.G.N
TRIAL       WHENEVER N.E.N/FAC*FAC, FUNCTION RETURN 0B
            FUNCTION RETURN 1B
            END OF FUNCTION

            PRINT COMMENT $ PRIMES UNDER 100 $
            THROUGH CAND, FOR C=0, 1, C.G.100
CAND        WHENEVER PRIME.(C), PRINT FORMAT PR,C
            VECTOR VALUES PR = $ I3*$

            END OF PROGRAM
Output:
PRIMES UNDER 100
  2
  3
  5
  7
 11
 13
 17
 19
 23
 29
 31
 37
 41
 43
 47
 53
 59
 61
 67
 71
 73
 79
 83
 89
 97

Maple

This could be coded in myriad ways; here is one.

TrialDivision := proc( n :: integer )
        if n <= 1 then
                false
        elif n = 2 then
                true
        elif type( n, 'even' ) then
                false
        else
                for local i from 3 by 2 while i * i <= n do
                        if irem( n, i ) = 0 then
                                return false
                        end if
                end do;
                true
        end if
end proc:

Using this to pick off the primes up to 30, we get:

> select( TrialDivision, [seq]( 1 .. 30 ) );
                  [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]

Here is a way to check that TrialDivision above agrees with Maple's built-in primality test (isprime).

> N := 10000: evalb( select( TrialDivision, [seq]( 1 .. N ) ) = select( isprime, [seq]( 1 .. N ) ) );
                                  true

Mathematica/Wolfram Language

IsPrime[n_Integer] := Block[{},
  If[n <= 1, Return[False]];
  If[n == 2, Return[True]]; If[Mod[n, 2] == 0, Return[False]];
  For[k = 3, k <= Sqrt[n], k += 2, If[Mod[n, k] == 0, Return[False]]];
  Return[True]]

MATLAB

function isPrime = primalityByTrialDivision(n)

    if n == 2
        isPrime = true;
        return
    elseif (mod(n,2) == 0) || (n <= 1)
        isPrime = false;
        return
    end
    
    %First n mod (3 to sqrt(n)) is taken. This will be a vector where the
    %first element is equal to n mod 3 and the last element is equal to n
    %mod sqrt(n). Then the all function is applied to that vector. If all
    %of the elements of this vector are non-zero (meaning n is prime) then
    %all() returns true. Otherwise, n is composite, so it returns false.
    %This return value is then assigned to the variable isPrime.
    isPrime = all(mod(n, (3:round(sqrt(n))) ));
    
end
Sample output:
>> arrayfun(@primalityByTrialDivision,(1:14))

ans =

     0     1     1     0     1     0     1     0     0     0     1     0     1     0

Maxima

isprme(n):= catch(
  for k: 2 thru sqrt(n) do if mod(n, k)=0 then throw(false),
  true);

map(isprme, [2, 3, 4, 65, 100, 181, 901]);
/* [true, true, false, false, false, true, false] */

min

Works with: min version 0.19.3
(
  :n 3 :i n sqrt :m true :p
  (i m <=) (
    (n i mod 0 ==) (m @i false @p) when
    i 2 + @i
  ) while p
) :_prime?  ; helper function

(
  (
    ((2 <) (false))
    ((dup even?) (2 ==))
    ((true) (_prime?))
  ) case
) :prime?

Miranda

main :: [sys_message]
main = [Stdout (show (filter prime [1..100])),
        Stdout "\n"]

prime :: num->bool
prime n = n=2 \/ n=3,                            if n<=4
        = False,                                 if n mod 2=0
        = #[d | d<-[3, 5..sqrt n]; n mod d=0]=0, otherwise
Output:
[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97]

МК-61/52

П0	1	-	x#0	34	2	-	/-/	x<0	32
ИП0	2	/	{x}	x#0	34
3	П4	ИП0	ИП4	/	{x}	x#0	34	КИП4	КИП4
ИП0	КвКор	ИП4	-	x<0	16	1	С/П	0	С/П

Modula-2

MODULE TrialDivision;
FROM InOut IMPORT WriteCard, WriteLn;

CONST
    Max = 100;
VAR
    i: CARDINAL;

PROCEDURE prime(n: CARDINAL): BOOLEAN;
VAR
    factor: CARDINAL;
BEGIN
    IF n <= 4 THEN
        RETURN (n = 2) OR (n = 3)
    ELSIF n MOD 2 = 0 THEN
        RETURN FALSE
    ELSE
        factor := 3;
        WHILE factor * factor <= n DO
            IF n MOD factor = 0 THEN
                RETURN FALSE
            END;
            INC(factor, 2)
        END
    END;
    RETURN TRUE
END prime;

BEGIN
    FOR i := 0 TO Max DO
        IF prime(i) THEN
            WriteCard(i,3);
            WriteLn
        END
    END
END TrialDivision.
Output:
  2
  3
  5
  7
 11
 13
 17
 19
 23
 29
 31
 37
 41
 43
 47
 53
 59
 61
 67
 71
 73
 79
 83
 89
 97

MUMPS

ISPRIME(N)
 QUIT:(N=2) 1
 NEW I,R
 SET R=N#2
 IF R FOR I=3:2:(N**.5) SET R=N#I Q:'R
 KILL I
 QUIT R

Usage (0 is false, nonzero is true):

USER>W $$ISPRIME^ROSETTA(2)
1
USER>W $$ISPRIME^ROSETTA(4)
0
USER>W $$ISPRIME^ROSETTA(7)
1
USER>W $$ISPRIME^ROSETTA(97)
7
USER>W $$ISPRIME^ROSETTA(99)
0

NetRexx

/* NetRexx */

options replace format comments java crossref savelog symbols nobinary

parse arg nbr rangeBegin rangeEnd .

if nbr = '' | nbr = '.' then do
  if rangeBegin = '' | rangeBegin = '.' then rangeBegin = 1
  if rangeEnd   = '' | rangeEnd   = '.' then rangeEnd   = 100
  if rangeEnd > rangeBegin then direction = 1
                           else direction = -1

  say 'List of prime numbers from' rangeBegin 'to' rangeEnd':'
  primes = ''
  loop nn = rangeBegin to rangeEnd by direction
    if isPrime(nn) then primes = primes nn
    end nn
    primes = primes.strip
    say '  'primes.changestr(' ', ',')
    say '  Total number of primes:' primes.words
  end
else do
  if isPrime(nbr) then say nbr.right(20) 'is prime'
                  else say nbr.right(20) 'is not prime'
  end

return

method isPrime(nbr = long) public static binary returns boolean

  ip = boolean

  select
    when nbr < 2 then do
      ip = isFalse
      end
    when '2 3 5 7'.wordpos(Rexx(nbr)) \= 0 then do
      -- crude shortcut ripped from the Rexx example
      ip = isTrue
      end
    when  nbr // 2 == 0 | nbr // 3 == 0 then do
      -- another shortcut permitted by the one above
      ip = isFalse
      end
    otherwise do
      nn = long
      nnStartTerm = long 3 -- a reasonable start term - nn <= 2 is never prime
      nnEndTerm = long Math.ceil(Math.sqrt(nbr)) -- a reasonable end term
      ip = isTrue -- prime the pump (pun intended)
      loop nn = nnStartTerm to nnEndTerm by 2
         -- Note: in Rexx and NetRexx "//" is the 'remainder of division operator' (which is not the same as modulo)
        if nbr // nn = 0 then do
          ip = isFalse
          leave nn
          end
        end nn
      end
    end

  return ip

method isTrue public static returns boolean
  return 1 == 1

method isFalse public static returns boolean
  return \isTrue
Output:
$ java -cp . RCPrimality 
List of prime numbers from 1 to 100:
  2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97
  Total number of primes: 25

$ java -cp . RCPrimality 91
                  91 is not prime

$ java -cp . RCPrimality 101
                 101 is prime

$ java -cp . RCPrimality . . 25
List of prime numbers from 1 to 25:
  2,3,5,7,11,13,17,19,23
  Total number of primes: 9

$ java -cp . RCPrimality . 9900 10010
List of prime numbers from 9900 to 10010:
  9901,9907,9923,9929,9931,9941,9949,9967,9973,10007,10009
  Total number of primes: 11

$ java -cp . RCPrimality . -57 1
List of prime numbers from -57 to 1:
  
  Total number of primes: 0

$ java -cp . RCPrimality . 100 -57
List of prime numbers from 100 to -57:
  97,89,83,79,73,71,67,61,59,53,47,43,41,37,31,29,23,19,17,13,11,7,5,3,2
  Total number of primes: 25

Rexx version reimplemented in NetRexx

Translation of: REXX
/* NetRexx */

options replace format comments java crossref savelog symbols nobinary

/*REXX program tests for primality using (kinda smartish) trial division*/

parse arg n .                          /*let user choose how many, maybe*/
if n=='' then n=10000                  /*if not, then assume the default*/
p=0                                    /*a count of primes  (so far).   */
                                       /*I like Heinz's 57 varieties... */
  loop j=-57 to n                      /*start in the cellar and work up*/
  if \isprime(j) then iterate          /*if not prime, keep looking.    */
  p=p+1                                /*bump the jelly bean counter.   */
  if j.length>2 then iterate           /*only show two-digit primes.    */
  say j.right(20) 'is prime.'          /*Just blab about the wee primes.*/
  end

say
say "there're" p "primes up to" n '(inclusive).'
exit

/*-------------------------------------ISPRIME subroutine---------------*/
method isprime(x) public static returns boolean
--isprime: procedure; arg x                   /*get the number in question*/
if '2 3 5 7'.wordpos(x)\==0 then return 1   /*is it a teacher's pet?    */
if x<2 | x//2==0 | x//3==0  then return 0   /*weed out the riff-raff.   */
                                            /*Note:   //  is modulus.   */
   loop j=5 by 6 until j*j>x                /*skips multiples of three. */
   if x//j==0 | x//(j+2)==0 then return 0   /*do a pair of divides (mod)*/
   end

return 1                                    /*I'm exhausted, it's prime!*/

newLISP

Short-circuit evaluation ensures that the many Boolean expressions are calculated in the right order so as not to waste time.

; Here are some simpler functions to help us:

(define (divisible? larger-number smaller-number)
	(zero? (% larger-number smaller-number)))

(define (int-root number)
	(floor (sqrt number)))

(define (even-prime? number)
	(= number 2))

; Trial division for odd numbers

(define (find-odd-factor? odd-number)
	(catch
		(for (possible-factor 3 (int-root odd-number) 2)
			(if (divisible? odd-number possible-factor)
				(throw true)))))

(define (odd-prime? number)
	(and
		(odd? number)
		(or
			(= number 3)
			(and
				(> number 3)
				(not (find-odd-factor? number))))))

; Now for the final overall Boolean function.

(define (is-prime? possible-prime)
	(or
		(even-prime? possible-prime)
		(odd-prime? possible-prime)))

; Let's use this to actually find some prime numbers.

(println (filter is-prime? (sequence 1 100)))
(exit)
Output:

(2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97)

Nim

Here are three ways to test primality using trial division.

import sequtils, math

proc prime(a: int): bool =
  if a == 2: return true
  if a < 2 or a mod 2 == 0: return false
  for i in countup(3, sqrt(a.float).int, 2):
    if a mod i == 0:
      return false
  return true

proc prime2(a: int): bool =
  result = not (a < 2 or any(toSeq(2 .. sqrt(a.float).int), a mod it == 0))

proc prime3(a: int): bool =
  if a == 2: return true
  if a < 2 or a mod 2 == 0: return false
  return not any(toSeq countup(3, sqrt(a.float).int, 2), a mod it == 0)

for i in 2..30:
  echo i, " ", prime(i)
Output:
2 true
3 true
4 false
5 true
6 false
7 true
8 false
9 false
10 false
11 true
12 false
13 true
14 false
15 false
16 false
17 true
18 false
19 true
20 false
21 false
22 false
23 true
24 false
25 false
26 false
27 false
28 false
29 true
30 false

Objeck

function : IsPrime(n : Int) ~ Bool {
  if(n <= 1) {
    return false;
  };
  
  for(i := 2; i * i <= n; i += 1;) {           
    if(n % i = 0) {
      return false;
    };
  };
  
  return true;
}

OCaml

let is_prime n =
  let rec test x =
    x * x > n || n mod x <> 0 && n mod (x + 2) <> 0 && test (x + 6)
  in
  if n < 5
  then n lor 1 = 3
  else n land 1 <> 0 && n mod 3 <> 0 && test 5

Octave

This function works on vectors and matrix.

function b = isthisprime(n)
  for r = 1:rows(n)
    for c = 1:columns(n)
      b(r,c) = false;
      if ( n(r,c) == 2 )
	b(r,c) = true;
      elseif ( (n(r,c) < 2) || (mod(n(r,c),2) == 0) )
	b(r,c) = false;
      else
	b(r,c) = true;
	for i = 3:2:sqrt(n(r,c))
	  if ( mod(n(r,c), i) == 0 )
	    b(r,c) = false;
	    break;
	  endif
	endfor
      endif
    endfor
  endfor
endfunction

% as test, print prime numbers from 1 to 100
p = [1:100];
pv = isthisprime(p);
disp(p( pv ));

Oforth

Integer method: isPrime
| i |
   self 1 <= ifTrue: [ false return ]
   self 3 <= ifTrue: [ true return ]
   self isEven ifTrue: [ false return ]
   3 self sqrt asInteger for: i [ self i mod ifzero: [ false return ] ]
   true ;
Output:
#isPrime 1000 seq filter println
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 8
9, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181
, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281
, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397
, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503
, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619
, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743
, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863
, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997
]

Ol

(define (prime? number)
   (define max (sqrt number))
   (define (loop divisor)
      (or (> divisor max)
          (and (> (modulo number divisor) 0)
               (loop (+ divisor 2)))))
   (or (= number 1)
       (= number 2)
       (and
          (> (modulo number 2) 0)
          (loop 3))))

Testing:

; first prime numbers less than 100
(for-each (lambda (n)
      (if (prime? n)
         (display n))
      (display " "))
   (iota 100))
(print)

; few more sintetic tests
(for-each (lambda (n)
      (print n " - prime? " (prime? n)))
   '(
      1234567654321 ; 1111111 * 1111111
      679390005787 ; really prime, I know that
      679390008337 ; same
      666810024403 ; 680633 * 979691 (multiplication of two prime numbers)
      12345676543211234567654321
      12345676543211234567654321123456765432112345676543211234567654321123456765432112345676543211234567654321
   ))
Output:
 1 2 3  5  7    11  13    17  19    23      29  31      37    41  43    47      53      59  61      67    71  73      79    83      89        97
1234567654321 - prime? #false
679390005787 - prime? #true
679390008337 - prime? #true
666810024403 - prime? #false
12345676543211234567654321 - prime? #false
12345676543211234567654321123456765432112345676543211234567654321123456765432112345676543211234567654321 - prime? #false

Oz

   fun {Prime N}
      local IPrime in
	 fun {IPrime N Acc}
	    if N < Acc*Acc then true
	    elseif (N mod Acc) == 0 then false
	    else {IPrime N Acc+1}
	    end
	 end
	 if N < 2 then false
	 else {IPrime N 2} end
      end
   end

Panda

In Panda you write a boolean function by making it filter, either returning it's input or nothing.

fun prime(p) type integer->integer
  p.gt(1) where q=p.sqrt NO(p.mod(2..q)==0)

1..100.prime

PARI/GP

trial(n)={
  if(n < 4, return(n > 1)); /* Handle negatives */
  forprime(p=2,sqrtint(n),
    if(n%p == 0, return(0))
  );
  1
};

Pascal

Translation of: QuickBASIC
program primes;

function prime(n: integer): boolean;
var
  i: integer; max: real;
begin
  if n = 2 then
    prime := true
  else if (n <= 1) or (n mod 2 = 0) then
    prime := false
  else begin
    prime := true; i := 3; max := sqrt(n);
    while i <= max do begin
      if n mod i = 0 then begin
        prime := false; exit
      end;
      i := i + 2
    end
  end
end;

{ Test and display primes 0 .. 50 }
var 
  n: integer;
begin
  for n := 0 to 50 do
    if (prime(n)) then
      write(n, ' ');
end.
Output:
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

improved using number wheel

Library: primTrial
Works with: Free Pascal
program TestTrialDiv;
{$IFDEF FPC}
  {$MODE DELPHI}{$Smartlink ON}
{$ELSE}
  {$APPLICATION CONSOLE}// for Delphi
{$ENDIF}
uses
  primtrial;
{ Test and display primes 0 .. 50 }
begin
  repeat
    write(actPrime,' ');
  until nextPrime > 50;
end.
Output
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

Perl

A simple idiomatic solution:

sub prime { my $n = shift || $_;
    $n % $_ or return for 2 .. sqrt $n;
    $n > 1
}

print join(', ' => grep prime, 1..100), "\n";

Excluding multiples of 2 and 3

One of many ways of writing trial division using a mod-6 wheel. Almost 2x faster than the simple method shown earlier.

sub isprime {
  my $n = shift;
  return ($n >= 2) if $n < 4;
  return unless $n % 2  &&  $n % 3;
  my $sqrtn = int(sqrt($n));
  for (my $i = 5; $i <= $sqrtn; $i += 6) {
    return unless $n % $i && $n % ($i+2);
  }
  1;
}
my $s = 0;
$s += !!isprime($_) for 1..100000;
print "Pi(100,000) = $s\n";

By Regular Expression

JAPH by Abigail 1999 [1] in conference slides 2000 [2].

While this is extremely clever and often used for Code golf, it should never be used for real work (it is extremely slow and uses lots of memory).

sub isprime {
  ('1' x shift) !~ /^1?$|^(11+?)\1+$/
}
print join(', ', grep(isprime($_), 0..39)), "\n";

Phix

function is_prime_by_trial_division(integer n)
    if n<2 then return 0 end if
    if n=2 then return 1 end if
    if remainder(n,2)=0 then return 0 end if
    for i=3 to floor(sqrt(n)) by 2 do
        if remainder(n,i)=0 then
            return 0
        end if
    end for
    return 1
end function
?filter(tagset(32),is_prime_by_trial_division)
Output:
{2,3,5,7,11,13,17,19,23,29,31}

PHP

<?php
function prime($a) {
  if (($a % 2 == 0 && $a != 2) || $a < 2)
    return false;
  $limit = sqrt($a);
  for ($i = 2; $i <= $limit; $i++)
    if ($a % $i == 0)
      return false;
  return true;
}

foreach (range(1, 100) as $x)
  if (prime($x)) echo "$x\n";

?>

By Regular Expression

<?php
function prime($a) {
  return !preg_match('/^1?$|^(11+?)\1+$/', str_repeat('1', $a));
}
?>

Picat

Here are four different versions.

Iterative

is_prime1(N) => 
  if N == 2 then
    true
  elseif N <= 1 ; N mod 2 == 0 then
    false
  else
    foreach(I in 3..2..ceiling(sqrt(N)))
       N mod I > 0
    end
  end.

Recursive

is_prime2(N) => 
  (N == 2 ; is_prime2b(N,3)).

is_prime2b(N,_Div), N <= 1 => false.
is_prime2b(2,_Div) => true.
is_prime2b(N,_Div), N mod 2 == 0 => false.
is_prime2b(N,Div), Div > ceiling(sqrt(N)) => true.
is_prime2b(N,Div), Div > 2 => 
 (N mod Div == 0 -> 
    false 
  ; 
    is_prime2b(N,Div+2)
  ).

Functional

is_prime3(2) => true.
is_prime3(3) => true.
is_prime3(P) => P > 3, P mod 2 =\= 0, not has_factor3(P,3).  

has_factor3(N,L), N mod L == 0 => true.
has_factor3(N,L) => L * L < N, L2 = L + 2, has_factor3(N,L2).

Generator approach

Translation of: Prolog

prime2(N) can be used to generate primes until memory is exhausted.

Difference from Prolog implementation: Picat does not support between/3 with "inf" as upper bound, so a high number (here 2**156+1) must be used.

prime2(2).
prime2(N) :-
  between(3, 2**156+1, N),
  N mod 2 = 1,              % odd
  M is floor(sqrt(N+1)),    % round-off paranoia 
  Max is (M-1) // 2,        % integer division
  foreach(I in 1..Max) N mod (2*I+1) > 0 end.

Test

go =>
  println([I : I in 1..100, is_prime1(I)]),
  nl,
  foreach(P in 1..6) 
     Primes = [ I : I in 1..10**P, is_prime1(I)],
     println([10**P,Primes.len])
  end,
  nl.


Output:
[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97]

[10,4]
[100,25]
[1000,168]
[10000,1229]
[100000,9592]
[1000000,78498]

Benchmark

Times for calculating the number of primes below 10, 100,1_000,10_000, 100_000, and 1_000_000 respectively.

  • imperative: is_prime1/1 (0.971)
  • recursive: is_prime2/1 (3.258s)
  • functional: is_prime3/1 (0.938s)
  • test/generate prime2/1 (2.129s)

PicoLisp

(de prime? (N)
   (or
      (= N 2)
      (and
         (> N 1)
         (bit? 1 N)
         (let S (sqrt N)
            (for (D 3  T  (+ D 2))
               (T (> D S) T)
               (T (=0 (% N D)) NIL) ) ) ) ) )

PL/0

The program waits for a number. Then it displays 1 if the number is prime, 0 otherwise.

var p, isprime;

procedure checkprimality;
var i, isichecked;
begin
  isprime := 0;
  if p = 2 then isprime := 1;
  if p >= 3 then
  begin
    i := 2; isichecked := 0;
    while isichecked = 0 do
    begin
      if (p / i) * i = p then isichecked := 1;
      if isichecked <> 1 then
        if i * i >= p then
        begin
          isprime := 1; isichecked := 1
        end;
      i := i + 1
    end
  end
end;

begin
  ? p;
  call checkprimality;
  ! isprime
end.

4 runs:

Input:
1
Output:
       0
Input:
25
Output:
       0
Input:
43
Output:
       1
Input:
101
Output:
       1

PL/I

is_prime: procedure (n) returns (bit(1));
   declare n fixed (15);
   declare i fixed (10);

   if n < 2 then return ('0'b);
   if n = 2 then return ('1'b);
   if mod(n, 2) = 0 then return ('0'b);

   do i = 3 to sqrt(n) by 2;
      if mod(n, i) = 0 then return ('0'b);
   end;
   return ('1'b);
end is_prime;

PL/M

This can be compiled with the original 8080 PL/M compiler and run under CP/M or an emulator or clone.
Note that all integers in 8080 PL/M are unsigned.

100H: /* TEST FOR PRIMALITY BY TRIAL DIVISION                                */

   DECLARE FALSE LITERALLY '0', TRUE LITERALLY '0FFH';
   /* CP/M BDOS SYSTEM CALL                                                  */
   BDOS: PROCEDURE( FN, ARG ); DECLARE FN BYTE, ARG ADDRESS; GOTO 5; END;
   PR$CHAR:   PROCEDURE( C ); DECLARE C BYTE;    CALL BDOS( 2, C );  END;
   PR$STRING: PROCEDURE( S ); DECLARE S ADDRESS; CALL BDOS( 9, S );  END;
   PR$NL:     PROCEDURE; CALL PR$STRING( .( 0DH, 0AH, '$' ) );       END;
   PR$NUMBER: PROCEDURE( N );
      DECLARE N ADDRESS;
      DECLARE V ADDRESS, N$STR( 6 ) BYTE, W BYTE;
      N$STR( W := LAST( N$STR ) ) = '$';
      N$STR( W := W - 1 ) = '0' + ( ( V := N ) MOD 10 );
      DO WHILE( ( V := V / 10 ) > 0 );
         N$STR( W := W - 1 ) = '0' + ( V MOD 10 );
      END;
      CALL PR$STRING( .N$STR( W ) );
   END PR$NUMBER;
   /* INTEGER SUARE ROOT: BASED ON THE ONE IN THE PL/M FOR FROBENIUS NUMBERS */
   SQRT: PROCEDURE( N )ADDRESS;
      DECLARE ( N, X0, X1 ) ADDRESS;
      IF N <= 3 THEN DO;
          IF N = 0 THEN X0 = 0; ELSE X0 = 1;
          END;
      ELSE DO;
         X0 = SHR( N, 1 );
         DO WHILE( ( X1 := SHR( X0 + ( N / X0 ), 1 ) ) < X0 );
            X0 = X1;
         END;
      END;
      RETURN X0;
   END SQRT;

   IS$PRIME: PROCEDURE( N )BYTE; /* RETURNS TRUE IF N IS PRIME, FALSE IF NOT */
      DECLARE N ADDRESS;
      IF N < 2 THEN RETURN FALSE;
      ELSE IF ( N AND 1 ) = 0 THEN RETURN N = 2;
      ELSE DO;
         /* ODD NUMBER > 2                                                   */
         DECLARE I ADDRESS;
         DO I = 3 TO SQRT( N ) BY 2;
            IF N MOD I = 0 THEN RETURN FALSE;
         END;
         RETURN TRUE;
      END;
   END IS$PRIME;

   /* TEST THE IS$PRIME PROCEDURE                                            */
   DECLARE I ADDRESS;
   DO I = 0 TO 100;
      IF IS$PRIME( I ) THEN DO;
         CALL PR$CHAR( ' ' );
         CALL PR$NUMBER( I );
      END;
   END;
   CALL PR$NL;

EOF
Output:
 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

PowerShell

function isPrime ($n) {
    if ($n -eq 1) {$false} 
    elseif ($n -eq 2) {$true}
    elseif ($n -eq 3) {$true}
    else{
        $m = [Math]::Floor([Math]::Sqrt($n))
        (@(2..$m | where {($_ -lt $n)  -and ($n % $_ -eq 0) }).Count -eq 0)
    }
}
1..15 | foreach{"isPrime $_ : $(isPrime $_)"}

Output:

isPrime 1 : False
isPrime 2 : True
isPrime 3 : True
isPrime 4 : False
isPrime 5 : True
isPrime 6 : False
isPrime 7 : True
isPrime 8 : False
isPrime 9 : False
isPrime 10 : False
isPrime 11 : True
isPrime 12 : False
isPrime 13 : True
isPrime 14 : False
isPrime 15 : False

Prolog

The following predicate showcases Prolog's support for writing predicates suitable for both testing and generating. In this case, assuming the Prolog implemenation supports indefinitely large integers, prime(N) can be used to generate primes until memory is exhausted.

prime(2).
prime(N) :- 
  between(3, inf, N),
  1 is N mod 2,             % odd
  M is floor(sqrt(N+1)),    % round-off paranoia 
  Max is (M-1) // 2,        % integer division
  forall( between(1, Max, I), N mod (2*I+1) > 0 ).

Example using SWI-Prolog:

?- time( (bagof( P, (prime(P), ((P > 100000, !, fail); true)), Bag),
       length(Bag,N),
       last(Bag,Last),
       writeln( (N,Last) ) )).

% 1,724,404 inferences, 1.072 CPU in 1.151 seconds (93% CPU, 1607873 Lips)
Bag = [2, 3, 5, 7, 11, 13, 17, 19, 23|...],
N = 9592,
Last = 99991.

?-  time( prime(99991) ).
% 165 inferences, 0.000 CPU in 0.000 seconds (92% CPU, 1213235 Lips)
true.

?-

Python

The simplest primality test, using trial division:

Works with: Python version 2.5
def prime(a):
    return not (a < 2 or any(a % x == 0 for x in xrange(2, int(a**0.5) + 1)))

Another test. Exclude even numbers first:

def prime2(a):
    if a == 2: return True
    if a < 2 or a % 2 == 0: return False
    return not any(a % x == 0 for x in xrange(3, int(a**0.5) + 1, 2))

Yet another test. Exclude multiples of 2 and 3, see http://www.devx.com/vb2themax/Tip/19051:

Works with: Python version 2.4
def prime3(a):
    if a < 2: return False
    if a == 2 or a == 3: return True # manually test 2 and 3   
    if a % 2 == 0 or a % 3 == 0: return False # exclude multiples of 2 and 3

    maxDivisor = a**0.5
    d, i = 5, 2
    while d <= maxDivisor:
        if a % d == 0: return False
        d += i 
        i = 6 - i # this modifies 2 into 4 and viceversa

    return True

By Regular Expression

Regular expression by "Abigail".
(An explanation is given in "The Story of the Regexp and the Primes").

>>> import re
>>> def isprime(n):
    return not re.match(r'^1?$|^(11+?)\1+$', '1' * n)

>>> # A quick test
>>> [i for i in range(40) if isprime(i)]
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]

Qi

(define prime?-0
  K N -> true where (> (* K K) N)
  K N -> false where (= 0 (MOD N K))
  K N -> (prime?-0 (+ K 2) N))

(define prime?
  1 -> false
  2 -> true
  N -> false where (= 0 (MOD N 2))
  N -> (prime?-0 3 N))

Quackery

sqrt+ is defined at Isqrt (integer square root) of X#Quackery.

  [ dup 4 < iff [ 1 > ] done
    dup 1 & not iff [ drop false ] done
    true swap dup sqrt+
    0 = iff [ 2drop not ] done
    1 >> times
      [ dup i^ 1 << 3 + mod 0 = if
          [ dip not conclude ] ]
    drop ]                              is isprime ( n --> b )

R

is.prime <- function(n) n == 2 || n > 2 && n %% 2 == 1 && (n < 9 || all(n %% seq(3, floor(sqrt(n)), 2) > 0))

which(sapply(1:100, is.prime))
# [1]  2  3  5  7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Racket

#lang racket

(define (prime? number)
  (cond ((not (positive? number)) #f)
        ((= 1 number) #f)
        ((even? number) (= 2 number))
        (else (for/and ((i (in-range 3 (ceiling (sqrt number)))))
                (not (zero? (remainder number i)))))))

Raku

(formerly Perl 6) Here we use a "none" junction which will autothread through the %% "is divisible by" operator to assert that $i is not divisible by 2 or any of the numbers up to its square root. Read it just as you would English: "Integer $i is prime if it is greater than one and is divisible by none of 2, 3, up to the square root of $i."

sub prime (Int $i --> Bool) {
    $i > 1 and so $i %% none 2..$i.sqrt;
}

This can easily be improved in two ways. First, we generate the primes so we only divide by those, instead of all odd numbers. Second, we memoize the result using the //= idiom of Perl, which does the right-hand calculation and assigns it only if the left side is undefined. We avoid recalculating the square root each time. Note the mutual recursion that depends on the implicit laziness of list evaluation:

my @primes = 2, 3, 5, -> $p { ($p+2, $p+4 ... &prime)[*-1] } ... *;
my @isprime = False,False;   # 0 and 1 are not prime by definition
sub prime($i) {
    my \limit = $i.sqrt.floor;
    @isprime[$i] //= so ($i %% none @primes ...^ { $_ > limit })
}

say "$_ is{ "n't" x !prime($_) } prime." for 1 .. 100;

REBOL

prime?: func [n] [
    case [
        n = 2 [ true  ]
        n <= 1 or (n // 2 = 0) [ false ]
        true [
            for i 3 round square-root n 2 [
                if n // i = 0 [ return false ]
            ]
            true
        ]
    ]
]
repeat i 100 [ print [i prime? i]]

REXX

compact version

This version uses a technique which increments by six for testing primality   (up to the   √ n ).

Programming note:   all the REXX programs below show all primes up and including the number specified.

  If the number is negative, the absolute value of it is used for the upper limit, but no primes are shown.
  The   number   of primes found is always shown.

Also, it was determined that computing the (integer) square root of the number to be tested in the   isPrime  
function slowed up the function   (for all three REXX versions),   however, for larger numbers of   N,   it would
be faster.

/*REXX program tests for  primality by using  (kinda smartish)  trial division.         */
parse arg n .;  if n==''  then n=10000           /*let the user choose the upper limit. */
tell=(n>0);     n=abs(n)                         /*display the primes  only if   N > 0. */
p=0                                              /*a count of the primes found (so far).*/
      do j=-57  to n                             /*start in the cellar and work up.     */
      if \isPrime(j)  then iterate               /*if not prime,  then keep looking.    */
      p=p+1                                      /*bump the jelly bean counter.         */
      if tell  then say right(j,20) 'is prime.'  /*maybe display prime to the terminal. */
      end   /*j*/
say
say  "There are "      p       " primes up to "        n        ' (inclusive).'
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
isPrime: procedure;    parse arg x                       /*get the number to be tested. */
         if wordpos(x, '2 3 5 7')\==0  then return 1     /*is number a teacher's pet?   */
         if x<2 | x//2==0 | x//3==0    then return 0     /*weed out the riff-raff.      */
            do k=5  by  6  until k*k>x                   /*skips odd multiples of  3.   */
            if x//k==0 | x//(k+2)==0   then return 0     /*a pair of divides.      ___  */
            end   /*k*/                                  /*divide up through the  √ x   */
                                                         /*Note:  //   is  ÷  remainder.*/
         return 1                                        /*done dividing, it's prime.   */
output   when using the default input of:   100
                   2 is prime.
                   3 is prime.
                   5 is prime.
                   7 is prime.
                  11 is prime.
                  13 is prime.
                  17 is prime.
                  19 is prime.
                  23 is prime.
                  29 is prime.
                  31 is prime.
                  37 is prime.
                  41 is prime.
                  43 is prime.
                  47 is prime.
                  53 is prime.
                  59 is prime.
                  61 is prime.
                  67 is prime.
                  71 is prime.
                  73 is prime.
                  79 is prime.
                  83 is prime.
                  89 is prime.
                  97 is prime.

There are  25  primes up to  100 (inclusive).

optimized version

This version separates multiple-clause   if   statements, and also tests for low primes,
making it about 8% faster.

/*REXX program tests for  primality by using  (kinda smartish)  trial division.         */
parse arg n .;  if n==''  then n=10000           /*let the user choose the upper limit. */
tell=(n>0);     n=abs(n)                         /*display the primes  only if   N > 0. */
p=0                                              /*a count of the primes found (so far).*/
      do j=-57  to n                             /*start in the cellar and work up.     */
      if \isPrime(j)  then iterate               /*if not prime,  then keep looking.    */
      p=p+1                                      /*bump the jelly bean counter.         */
      if tell  then say right(j,20) 'is prime.'  /*maybe display prime to the terminal. */
      end   /*j*/
say
say  "There are "      p       " primes up to "        n        ' (inclusive).'
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
isPrime: procedure;  parse arg x                       /*get integer to be investigated.*/
         if x<11     then return wordpos(x, '2 3 5 7')\==0         /*is it a wee prime? */
         if x//2==0  then return 0                     /*eliminate all the even numbers.*/
         if x//3==0  then return 0                     /* ··· and eliminate the triples.*/
                  do k=5  by 6  until k*k>x            /*this skips odd multiples of 3. */
                  if x//k    ==0  then return 0        /*perform a divide (modulus),    */
                  if x//(k+2)==0  then return 0        /* ··· and the next umpty one.   */
                  end   /*k*/                          /*Note: REXX  //  is ÷ remainder.*/
         return 1                                      /*did all divisions, it's prime. */
output   is identical to the first version when the same input is used.

unrolled version

This version uses an unrolled version (of the 2nd version) of some multiple-clause   if   statements, and
also an optimized version of the testing of low primes is used, making it about 22% faster.

Note that the   do ... until ...   was changed to   do ... while ....

/*REXX program tests for  primality by using  (kinda smartish)  trial division.         */
parse arg n .;  if n==''  then n=10000           /*let the user choose the upper limit. */
tell=(n>0);     n=abs(n)                         /*display the primes  only if   N > 0. */
p=0                                              /*a count of the primes found (so far).*/
      do j=-57  to n                             /*start in the cellar and work up.     */
      if \isPrime(j)  then iterate               /*if not prime,  then keep looking.    */
      p=p+1                                      /*bump the jelly bean counter.         */
      if tell  then say right(j,20) 'is prime.'  /*maybe display prime to the terminal. */
      end   /*j*/
say
say  "There are "      p       " primes up to "        n        ' (inclusive).'
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
isPrime: procedure;    parse arg x               /*get the integer to be investigated.  */
         if x<107  then return wordpos(x, '2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53',
                           '59 61 67 71 73 79 83 89 97 101 103')\==0  /*some low primes.*/
         if x// 2 ==0  then return 0             /*eliminate all the even numbers.      */
         if x// 3 ==0  then return 0             /* ··· and eliminate the triples.      */
         parse var  x  ''  -1  _                 /*          obtain the rightmost digit.*/
         if     _ ==5  then return 0             /* ··· and eliminate the nickels.      */
         if x// 7 ==0  then return 0             /* ··· and eliminate the luckies.      */
         if x//11 ==0  then return 0
         if x//13 ==0  then return 0
         if x//17 ==0  then return 0
         if x//19 ==0  then return 0
         if x//23 ==0  then return 0
         if x//29 ==0  then return 0
         if x//31 ==0  then return 0
         if x//37 ==0  then return 0
         if x//41 ==0  then return 0
         if x//43 ==0  then return 0
         if x//47 ==0  then return 0
         if x//53 ==0  then return 0
         if x//59 ==0  then return 0
         if x//61 ==0  then return 0
         if x//67 ==0  then return 0
         if x//71 ==0  then return 0
         if x//73 ==0  then return 0
         if x//79 ==0  then return 0
         if x//83 ==0  then return 0
         if x//89 ==0  then return 0
         if x//97 ==0  then return 0
         if x//101==0  then return 0
         if x//103==0  then return 0             /*Note:  REXX   //   is  ÷  remainder. */
                   do k=107  by 6  while k*k<=x  /*this skips odd multiples of three.   */
                   if x//k    ==0  then return 0 /*perform a divide (modulus),          */
                   if x//(k+2)==0  then return 0 /* ··· and the next also.   ___        */
                   end   /*k*/                   /*divide up through the    √ x         */
         return 1                                /*after all that,  ··· it's a prime.   */
output   is identical to the first version when the same input is used.


Ring

give n 
flag = isPrime(n)
if flag = 1 see n + " is a prime number" 
else see n + " is not a prime number" ok

func isPrime num
     if (num <= 1) return 0 ok
     if (num % 2 = 0 and num != 2) return 0 ok
     for i = 3 to floor(num / 2) -1 step 2
         if (num % i = 0) return 0 ok
     next
     return 1

RPL

Translation of: Python

This version use binary integers

Works with: Halcyon Calc version 4.2.7
RPL code Comment
≪ / LAST ROT * - #0 == ≫ 'BDIV?' STO

≪ 
   IF DUP #3 ≤ THEN #2 / B→R
   ELSE
      IF DUP #2 BDIV? OVER #3 BDIV? OR
      THEN DROP 0
      ELSE 
        DUP B→R √ R→B → a maxd 
        ≪ a #2 #5 1 SF
           WHILE 1 FS? OVER maxd ≤ AND REPEAT 
              IF a OVER BDIV? THEN 1 CF END
              OVER + #6 ROT - SWAP END
        ≫
      SWAP DROP BDIV? NOT 
      END
   END
≫ 'BPRIM?' STO
BDIV? ( #a #b -- boolean ) 

BPRIM? ( #a -- boolean )
return 1 if a is 2 or 3

if 2 or 3 divides a
  return 0   
else
  store a and root(a)
  initialize stack with a i d and set flag 1 to control loop exit
  while d <= root(a)
       prepare loop exit if d divides a 
       i = 6 - i which modifies 2 into 4 and viceversa

  empty stack and return result



Floating point version

Faster but limited to 1E12.

IF DUP 5 ≤ THEN { 2 3 5 } SWAP POS 
   ELSE
     IF DUP 2 MOD NOT THEN 2
     ELSE
        DUP √ CEIL → lim 
        ≪ 3 WHILE DUP2 MOD OVER lim ≤ AND REPEAT 2 + ENDEND MOD 
  END SIGN
≫ 'PRIM?' STO

Ruby

def prime(a)
  if a == 2
    true
  elsif a <= 1 || a % 2 == 0
    false
  else
    divisors = (3..Math.sqrt(a)).step(2)
    divisors.none? { |d| a % d == 0 }
  end
end
p (1..50).select{|i| prime(i)}

The prime package in the stdlib for Ruby contains this compact Prime#prime? method:

require "prime"
def prime?(value, generator = Prime::Generator23.new)
  return false if value < 2
  for num in generator
    q,r = value.divmod num
    return true if q < num
    return false if r == 0
  end
end
p (1..50).select{|i| prime?(i)}

Without any fancy stuff:

def primes(limit)
  (enclose = lambda { |primes|
    primes.last.succ.upto(limit) do |trial_pri|
      if primes.none? { |pri| (trial_pri % pri).zero? }
        return enclose.call(primes << trial_pri)
      end
    end
    primes
  }).call([2])
end
p primes(50)
Output:
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

By Regular Expression

def isprime(n)
  '1'*n !~ /^1?$|^(11+?)\1+$/
end

Prime Generators Tests

Mathematicaly basis of Prime Generators
https://www.academia.edu/19786419/PRIMES-UTILS_HANDBOOK 
https://www.academia.edu/42734410/Improved_Primality_Testing_and_Factorization_in_Ruby_revised
require "benchmark/ips"

# the simplest PG primality test using the P3 prime generator
# reduces the number space for primes to 2/6 (33.33%) of all integers

def primep3?(n)                           # P3 Prime Generator primality test
  # P3 = 6*k + {5, 7}                     # P3 primes candidates (pc) sequence
  return n | 1 == 3 if n < 5              # n: 0,1,4|false, 2,3|true 
  return false if n.gcd(6) != 1           # 1/3 (2/6) of integers are P3 pc
  p, sqrtn = 5, Integer.sqrt(n)           # first P3 sequence value
  until p > sqrtn
    return false if n % p == 0 || n % (p + 2) == 0  # if n is composite
    p += 6      # first prime candidate for next kth residues group
  end
  true
end

# PG primality test using the P5 prime generator
# reduces the number space for primes to 8/30 (26.67%) of all integers

def primep5?(n)                           # P5 Prime Generator primality test
   # P5 = 30*k + {7,11,13,17,19,23,29,31} # P5 primes candidates sequence
   return [2, 3, 5].include?(n) if n < 7  # for small and negative values
   return false if n.gcd(30) != 1         # 4/15 (8/30) of integers are P5 pc
   p, sqrtn = 7, Integer.sqrt(n)          # first P5 sequence value
   until p > sqrtn
     return false if                      # if n is composite
       n % (p)    == 0 || n % (p+4)  == 0 || n % (p+6)  == 0 || n % (p+10) == 0 ||
       n % (p+12) == 0 || n % (p+16) == 0 || n % (p+22) == 0 || n % (p+24) == 0
       p += 30  # first prime candidate for next kth residues group
   end
   true
end

# PG primality test using the P7 prime generator
# reduces the number space for primes to 48/210 (22.86%) of all integers

def primep7?(n)
  # P7 = 210*k + {11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,
  #      89,97,101,103,107,109,113,121,127,131,137,139,143,149,151,157,163,
  #      167,169,173,179,181,187,191,193,197,199,209,211}
  return [2, 3, 5, 7].include?(n) if n < 11  
  return false if n.gcd(210) != 1         # 8/35 (48/210) of integers are P7 pc
  p, sqrtn = 11, Integer.sqrt(n)          # first P7 sequence value
  until p > sqrtn
    return false if
      n % (p)     == 0 || n % (p+2)   == 0 || n % (p+6)   == 0 || n % (p+8)   == 0 ||
      n % (p+12)  == 0 || n % (p+18)  == 0 || n % (p+20)  == 0 || n % (p+26)  == 0 ||
      n % (p+30)  == 0 || n % (p+32)  == 0 || n % (p+36)  == 0 || n % (p+42)  == 0 ||
      n % (p+48)  == 0 || n % (p+50)  == 0 || n % (p+56)  == 0 || n % (p+60)  == 0 ||
      n % (p+62)  == 0 || n % (p+68)  == 0 || n % (p+72)  == 0 || n % (p+78)  == 0 ||
      n % (p+86)  == 0 || n % (p+90)  == 0 || n % (p+92)  == 0 || n % (p+96)  == 0 ||
      n % (p+98)  == 0 || n % (p+102) == 0 || n % (p+110) == 0 || n % (p+116) == 0 ||
      n % (p+120) == 0 || n % (p+126) == 0 || n % (p+128) == 0 || n % (p+132) == 0 ||
      n % (p+138) == 0 || n % (p+140) == 0 || n % (p+146) == 0 || n % (p+152) == 0 ||
      n % (p+156) == 0 || n % (p+158) == 0 || n % (p+162) == 0 || n % (p+168) == 0 ||
      n % (p+170) == 0 || n % (p+176) == 0 || n % (p+180) == 0 || n % (p+182) == 0 ||
      n % (p+186) == 0 || n % (p+188) == 0 || n % (p+198) == 0 || n % (p+200) == 0
    p += 210    # first prime candidate for next  kth residues group 
  end
  true
end

# Benchmarks to test for various size primes

p = 541
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    b.compare!
    puts
end

p = 1000003
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    b.compare!
    puts
end

p = 4294967291            # largest prime < 2**32
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    b.compare!
    puts
end

p = (10 ** 16) * 2 + 3
Benchmark.ips do |b|
    print "\np = #{p}"
    b.report("primep3?") { primep3?(p) }
    b.report("primep5?") { primep5?(p) }
    b.report("primep7?") { primep7?(p) }
    b.compare!
    puts
end
Output:
p = 541
Warming up --------------------------------------
            primep3?   109.893k i/100ms
            primep5?   123.949k i/100ms
            primep7?    44.216k i/100ms
Calculating -------------------------------------
            primep3?      1.598M (± 3.4%) i/s -      8.022M in   5.025036s
            primep5?      1.872M (± 6.3%) i/s -      9.420M in   5.059896s
            primep7?    502.040k (± 1.2%) i/s -      2.520M in   5.020919s

Comparison:
            primep5?:  1871959.0 i/s
            primep3?:  1598489.8 i/s - 1.17x  slower
            primep7?:   502039.8 i/s - 3.73x  slower


p = 1000003
Warming up --------------------------------------
            primep3?     5.850k i/100ms
            primep5?     9.013k i/100ms
            primep7?    10.889k i/100ms
Calculating -------------------------------------
            primep3?     59.965k (± 1.1%) i/s -    304.200k in   5.073641s
            primep5?     92.561k (± 2.1%) i/s -    468.676k in   5.065709s
            primep7?    109.335k (± 0.8%) i/s -    555.339k in   5.079549s

Comparison:
            primep7?:   109334.7 i/s
            primep5?:    92561.4 i/s - 1.18x  slower
            primep3?:    59964.5 i/s - 1.82x  slower


p = 4294967291
Warming up --------------------------------------
            primep3?    92.000  i/100ms
            primep5?   148.000  i/100ms
            primep7?   184.000  i/100ms
Calculating -------------------------------------
            primep3?    926.647  (± 1.1%) i/s -      4.692k in   5.064067s
            primep5?      1.480k (± 1.7%) i/s -      7.400k in   5.001399s
            primep7?      1.804k (± 1.0%) i/s -      9.200k in   5.099110s

Comparison:
            primep7?:     1804.4 i/s
            primep5?:     1480.0 i/s - 1.22x  slower
            primep3?:      926.6 i/s - 1.95x  slower


p = 20000000000000003
Warming up --------------------------------------
            primep3?     1.000  i/100ms
            primep5?     1.000  i/100ms
            primep7?     1.000  i/100ms
Calculating -------------------------------------
            primep3?      0.422  (± 0.0%) i/s -      3.000  in   7.115929s
            primep5?      0.671  (± 0.0%) i/s -      4.000  in   5.957077s
            primep7?      0.832  (± 0.0%) i/s -      5.000  in   6.007834s

Comparison:
            primep7?:        0.8 i/s
            primep5?:        0.7 i/s - 1.24x  slower
            primep3?:        0.4 i/s - 1.97x  slower

Rust

fn is_prime(n: u64) -> bool {
    match n {
        0 | 1 => false,
        2 => true,
        _even if n % 2 == 0 => false,
        _ => {
            let sqrt_limit = (n as f64).sqrt() as u64;
            (3..=sqrt_limit).step_by(2).find(|i| n % i == 0).is_none()
        }
    }
}

fn main() {
    for i in (1..30).filter(|i| is_prime(*i)) {
        println!("{} ", i);
    }
}
Output:
2 3 5 7 11 13 17 19 23 29 


S-lang

define is_prime(n)
{
   if (n == 2) return(1);
   if (n <= 1) return(0);
   if ((n & 1) == 0) return(0);

   variable mx = int(sqrt(n)), i;
   
   _for i (3, mx, 1) {
     if ((n mod i) == 0)
       return(0);
   }
   return(1);
}

define ptest() 
{
   variable lst = {};

   _for $1 (1, 64, 1)
     if (is_prime($1))
       list_append(lst, string($1));
   print(strjoin(list_to_array(lst), ", "));
}
ptest();
Output:
"2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61"

SAS

data primes;
do n=1 to 1000;
  link primep;
  if primep then output;
end;
stop;

primep:
if n < 4 then do;
  primep=n=2 or n=3;
  return;
end;
primep=0;
if mod(n,2)=0 then return;
do k=3 to sqrt(n) by 2;
  if mod(n,k)=0 then return;
end;
primep=1;
return;
keep n;
run;

Scala

Simple version

  def isPrime(n: Int) =
    n > 1 && (Iterator.from(2) takeWhile (d => d * d <= n) forall (n % _ != 0))

Accelerated version FP and parallel runabled

//
Output:
Best seen running in your browser Scastie (remote JVM).
object IsPrimeTrialDivision extends App {
  def isPrime(n: Long) =
    n > 1 && ((n & 1) != 0 || n == 2) && (n % 3 != 0 || n == 3) &&
      (5 to math.sqrt(n).toInt by 6).par.forall(d => n % d != 0 && n % (d + 2) != 0)

  assert(!isPrime(-1))
  assert(!isPrime(1))
  assert(isPrime(2))
  assert(isPrime(100000000003L))
  assert(isPrime(100000000019L))
  assert(isPrime(100000000057L))
  assert(isPrime(100000000063L))
  assert(isPrime(100000000069L))
  assert(isPrime(100000000073L))
  assert(isPrime(100000000091L))
  println("10 Numbers tested. A moment please …\nNumber crunching biggest 63-bit prime …")
  assert(isPrime(9223372036854775783L)) // Biggest 63-bit prime
  println("All done")

}

Accelerated version FP, tail recursion

Tests 1.3 M numbers against OEIS prime numbers.

import scala.annotation.tailrec
import scala.io.Source

object PrimesTestery extends App {
  val rawText = Source.fromURL("https://oeis.org/A000040/a000040.txt")
  val oeisPrimes = rawText.getLines().take(100000).map(_.split(" ")(1)).toVector

  def isPrime(n: Long) = {
    @tailrec
    def inner(d: Int, end: Int): Boolean = {
      if (d > end) true
      else if (n % d != 0 && n % (d + 2) != 0) inner(d + 6, end) else false
    }

    n > 1 && ((n & 1) != 0 || n == 2) &&
      (n % 3 != 0 || n == 3) && inner(5, math.sqrt(n).toInt)
  }

  println(oeisPrimes.size)
  for (i <- 0 to 1299709) assert(isPrime(i) == oeisPrimes.contains(i.toString), s"Wrong $i")

}

Scheme

Works with: Scheme version R RS
(define (prime? number)
  (define (*prime? divisor)
    (or (> (* divisor divisor) number)
        (and (> (modulo number divisor) 0)
             (*prime? (+ divisor 1)))))
  (and (> number 1)
       (*prime? 2)))
; twice faster, testing only odd divisors
(define (prime? n)
  (if (< n 4) (> n 1)
      (and (odd? n)
	   (let loop ((k 3))
	     (or (> (* k k) n)
		 (and (positive? (remainder n k))
		      (loop (+ k 2))))))))

Seed7

const func boolean: isPrime (in integer: number) is func
  result
    var boolean: prime is FALSE;
  local
    var integer: upTo is 0;
    var integer: testNum is 3;
  begin
    if number = 2 then
      prime := TRUE;
    elsif odd(number) and number > 2 then
      upTo := sqrt(number);
      while number rem testNum <> 0 and testNum <= upTo do
        testNum +:= 2;
      end while;
      prime := testNum > upTo;
    end if;
  end func;

Original source: [3]

Sidef

func is_prime(a) {
  given (a) {
    when (2)                   { true  }
    case (a <= 1 || a.is_even) { false }
    default                    { 3 .. a.isqrt -> any { .divides(a) } -> not }
  }
}
Translation of: Perl

Alternative version, excluding multiples of 2 and 3:

func is_prime(n) {
    return (n >= 2) if (n < 4)
    return false if (n%%2 || n%%3)
    for k in (5 .. n.isqrt -> by(6)) {
        return false if (n%%k || n%%(k+2))
    }
    return true
}

Smalltalk

| isPrime |
isPrime := [:n |
    n even ifTrue: [ ^n=2 ]
    ifFalse: [
        3 to: n sqrt do: [:i |
            (n \\ i = 0) ifTrue: [ ^false ]
        ].
        ^true
    ]
]

SNOBOL4

define('isprime(n)i,max') :(isprime_end)
isprime isprime = n
        le(n,1) :s(freturn)
        eq(n,2) :s(return)
        eq(remdr(n,2),0) :s(freturn)
        max = sqrt(n); i = 1
isp1    i = le(i + 2,max) i + 2 :f(return)
        eq(remdr(n,i),0) :s(freturn)f(isp1)
isprime_end

By Patterns

Using the Abigail regex transated to Snobol patterns.

        define('rprime(n)str,pat1,pat2,m1') :(end_rprime)
rprime  str = dupl('1',n); rprime = n
        pat1 = ('1' | '')
        pat2 = ('11' arbno('1')) $ m1 (*m1 arbno(*m1))
        str pos(0) (pat1 | pat2) rpos(0) :s(freturn)f(return)
end_rprime

*       # Test and display primes 0 .. 50
loop    rprimes = rprimes rprime(n)  ' '
        n = lt(n,50) n + 1 :s(loop)
        output = rprimes 
end
Output:
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

SparForte

As a structured script.

#!/usr/local/bin/spar
pragma annotate( summary, "prime" );
pragma annotate( description, "Write a boolean function that tells whether a given" );
pragma annotate( description, "integer is prime. Remember that 1 and all" );
pragma annotate( description, "non-positive numbers are not prime. " );
pragma annotate( see_also, "http://rosettacode.org/wiki/Primality_by_trial_division" );
pragma annotate( author, "Ken O. Burtch" );
pragma license( unrestricted );

pragma restriction( no_external_commands );

procedure prime is

function is_prime(item : positive) return boolean is
   result : boolean := true;
   test : natural;
begin
   if item /= 2 and item mod 2 = 0 then
      result := false;
   else
      test := 3;
      while test < natural( numerics.sqrt( item ) ) loop
         if natural(item) mod test = 0 then
            result := false;
            exit;
         end if;
         test := @ + 2;
      end loop;
  end if;
  return result;
end is_prime;

  number : positive;
  result : boolean;

begin
  number := 6;
  result   := is_prime( number );
  put( number ) @ ( " : " ) @ ( result );
  new_line;

  number := 7;
  result   := is_prime( number );
  put( number ) @ ( " : " ) @ ( result );
  new_line;

  number := 8;
  result   := is_prime( number );
  put( number ) @ ( " : " ) @ ( result );
  new_line;
end prime;

SQL

Works with: T-SQL
declare @number int
set @number = 514229 -- number to check

;with cte(number) as 
(
 select 2
 union all
 select number+1
 from cte
 where number+1 < @number
)
select
      cast(@number as varchar(100)) +
      case 
          when exists
				  (
					select * 
					from 
					(
						select number, @number % number modNumber
						from cte
					) tmp
					where tmp.modNumber = 0 
				  ) 
				          then ' is composite'
		  else
						 ' is prime'
	  end primalityTest
option (maxrecursion 0)

Standard ML

fun is_prime n =
  if n = 2 then true
  else if n < 2 orelse n mod 2 = 0 then false
  else let
    fun loop k =
      if k * k > n then true
      else if n mod k = 0 then false
      else loop (k+2)
    in loop 3
  end

Swift

import Foundation

extension Int {
  func isPrime() -> Bool {
    
    switch self {
    case let x where x < 2:
      return false
    case 2:
      return true
    default:
      return
        self % 2 != 0 &&
        !stride(from: 3, through: Int(sqrt(Double(self))), by: 2).contains {self % $0 == 0}
    }
  }
}

A version that works with Swift 5.x and probably later. Does not need to import Foundation

extension Int
{
	func isPrime() -> Bool
	{
		if self < 3
		{
			return self == 2
		}
		else
		{
			let upperLimit = Int(Double(self).squareRoot())
			return !self.isMultiple(of: 2) && !stride(from: 3, through: upperLimit, by: 2)
				.contains(where: { factor in self.isMultiple(of: factor) })
		}
	}
}

Tcl

proc is_prime n {
    if {$n <= 1} {return false}
    if {$n == 2} {return true}
    if {$n % 2 == 0} {return false}
    for {set i 3} {$i <= sqrt($n)} {incr i 2} {
        if {$n % $i == 0} {return false}
    }
    return true
}

UNIX Shell

Translation of: C
Works with: bash
Works with: ksh93
Works with: pdksh
Works with: zsh
function primep {
	typeset n=$1 p=3
	(( n == 2 )) && return 0	# 2 is prime.
	(( n & 1 )) || return 1		# Other evens are not prime.
	(( n >= 3 )) || return 1

	# Loop for odd p from 3 to sqrt(n).
	# Comparing p * p <= n can overflow.
	while (( p <= n / p )); do
		# If p divides n, then n is not prime.
		(( n % p )) || return 1
		(( p += 2 ))
	done
	return 0	# Yes, n is prime.
}
Works with: Bourne Shell
primep() {
	set -- "$1" 3
	test "$1" -eq 2 && return 0		# 2 is prime.
	expr "$1" \% 2 >/dev/null || return 1	# Other evens are not prime.
	test "$1" -ge 3 || return 1

	# Loop for odd p from 3 to sqrt(n).
	# Comparing p * p <= n can overflow. We use p <= n / p.
	while expr $2 \<= "$1" / $2 >/dev/null; do
		# If p divides n, then n is not prime.
		expr "$1" % $2 >/dev/null || return 1
		set -- "$1" `expr $2 + 2`
	done
	return 0	# Yes, n is prime.
}

Ursala

Excludes even numbers, and loops only up to the approximate square root or until a factor is found.

#import std
#import nat

prime = ~<{0,1}&& -={2,3}!| ~&h&& (all remainder)^Dtt/~& iota@K31

Test program to try it on a few numbers:

#cast %bL

test = prime* <5,6,7>
Output:
<true,false,true>

V

Translation of: Joy
[prime?
     2
     [[dup * >] [true] [false] ifte [% 0 >] dip and]
       [succ]
     while
     dup * <].
Using it:
|11 prime?
=true
|4 prime?
=false


Verilog

module main;
integer i, k;
  initial begin
    $display("Prime numbers between 0 and 100:");
    for(i = 2; i <= 99; i=i+1) begin
      k=i;
      if(i[0] != 1'b0) begin
        if(k==3 | k==5 | k==7 | k==11 | k==13 | k==17 | k==19)                    $write(i);
        else if(k%3==0 | k%5==0 | k%7==0 | k%11==0 | k%13==0 | k%17==0 | k%19==0) $write("");
             else                                                                 $write(i);
      end
      if(i==10'b00 | i==10'b010)                                                  $write(i);
    end
    $finish;
  end
endmodule

V (Vlang)

import math

const numbers = [5, 3, 14, 19, 25, 59, 88]

fn main() {
	for num in numbers {
		println("${num} is a prime number? " + if is_prime(num) == true {'yes'} else {'no'})
	}
}

fn is_prime(num int) bool {
     if num <= 1 {return false}
     if num % 2 == 0 && num != 2 {return false}
	 for idx := 3; idx <= math.floor(num / 2) - 1; idx += 2 {
         if num % idx == 0 {return false}
     }
     return true
}
Output:
5 is a prime number? yes
3 is a prime number? yes
14 is a prime number? no
19 is a prime number? yes
25 is a prime number? no
59 is a prime number? yes
88 is a prime number? no

Wren

Library: Wren-fmt
import "./fmt" for Fmt

var isPrime = Fn.new { |n|
    if (n < 2) return false
    if (n%2 == 0) return n == 2
    var p = 3
    while (p * p <= n) {
        if (n%p == 0) return false
        p = p + 2
    }
    return true
}

var tests = [2, 5, 12, 19, 57, 61, 97]
System.print("Are the following prime?")
for (test in tests) {
    Fmt.print("$2d -> $y", test, isPrime.call(test))
}
Output:
Are the following prime?
 2 -> yes
 5 -> yes
12 -> no
19 -> yes
57 -> no
61 -> yes
97 -> yes

XPL0

func Prime(N);          \Return 'true' if N is a prime number
int  N;
int  I;
[if N <= 1 then return false;
for I:= 2 to sqrt(N) do
        if rem(N/I) = 0 then return false;
return true;
];

int  Num;
repeat  Num:= IntIn(0);
        Text(0, if Prime(Num) then "is " else "not ");
        Text(0, "prime^M^J");
until   Num = 0
Output:
777777777
not prime
777777773
is prime
0
not prime

zkl

The Method filter1 stops at the first non False result, which, if there is one, is the first found diviser, thus short cutting the rest of the test

fcn isPrime(n){
   if(n.isEven or n<2) return(n==2); 
   (not [3..n.toFloat().sqrt().toInt(),2].filter1('wrap(m){n%m==0}))
}
Output:
zkl: [1..].filter(20,isPrime)
L(2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71)
zkl: isPrime(777777773)
True
zkl: isPrime(777777777)
False