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Task

Find squares n where n+1 is prime and n<1.000

ALGOL 68

<lang algol68>BEGIN # find squares n where n + 1 is prime #

   PR read "primes.incl.a68" PR
   []BOOL prime = PRIMESIEVE 1 000; # construct a sieve of primes up to 1000 #
   # find the squares 1 less than a prime (ignoring squares of non-integers) #
   # other than 1, the numbers must be even                                  #
   IF prime[ 2 # i.e.: ( 1 * 1 ) + 1 # ] THEN print( ( " 1" ) ) FI;
   FOR i FROM 2 BY 2 TO UPB prime WHILE INT i2 = i * i;
                                        i2 < UPB prime
   DO
       IF prime[ i2 + 1 ] THEN
           print( ( " ", whole( i2, 0 ) ) )
       FI
   OD

END</lang>

Output:

 1 4 16 36 100 196 256 400 576 676

AutoHotkey

Translation of: FreeBASIC

<lang AutoHotkey>n := 0 while ((n2 := (n+=2)**2) < 1000)

   if isPrime(n2+1)
       result .= (result ? ", ":"" ) n2

MsgBox % result := 1 ", " result return

isPrime(n, i:=2){

   while (i < Sqrt(n)+1)
       if !Mod(n, i++)
           return False
   return True

}</lang>

Output:

1, 4, 16, 36, 100, 196, 256, 400, 576, 676

AWK

syntax: GAWK -f FIND_SQUARES_N_WHERE_N+1_IS_PRIME.AWK

BEGIN {

   start = 1
   stop = 999
   n = 2
   n2 = n^2
   printf("1")
   count++
   while (n2 < stop) {
     if (is_prime(n2+1)) {
       printf(" %d",n2)
       count++
     }
     n += 2
     n2 = n^2
   }
   printf("\nFind squares %d-%d: %d\n",start,stop,count)
   exit(0)

} function is_prime(n, d) {

   d = 5
   if (n < 2) { return(0) }
   if (n % 2 == 0) { return(n == 2) }
   if (n % 3 == 0) { return(n == 3) }
   while (d*d <= n) {
     if (n % d == 0) { return(0) }
     d += 2
     if (n % d == 0) { return(0) }
     d += 4
   }
   return(1)

} </lang>

Output:

1 4 16 36 100 196 256 400 576 676
Find squares 1-999: 10

<lang basic>10 DEFINT A-Z: N=1000 20 DIM C(N) 30 FOR P=2 TO SQR(N) 40 IF NOT C(P) THEN FOR C=P*P TO N STEP P: C(C)=1=1: NEXT 50 NEXT 60 FOR I=2 TO N 70 IF C(I) THEN 100 80 X=I-1: R=SQR(X) 90 IF R*R=X THEN PRINT X; 100 NEXT</lang>

Output:

 1  4  16  36  100  196  256  400  576  676

BCPL

<lang bcpl>get "libhdr" manifest $( MAX = 1000 $)

let isqrt(s) = valof $( let x0 = s>>1 and x1 = ?

   if x0 = 0 resultis s
   x1 := (x0 + s/x0)>>1
   while x1<x0
   $(  x0 := x1
       x1 := (x0 + s/x0)>>1
   $)
   resultis x0

$)

let sieve(prime, n) be $( 0!prime := false

   1!prime := false
   for i = 2 to n do i!prime := true
   for p = 2 to isqrt(n) if p!prime
   $(  let c = p*p
       while c<n
       $(  c!prime := false
           c := c + p
       $)
   $)

$)

let square(n) = valof $( let sq = isqrt(n)

   resultis sq*sq = n

$)

let start() be $( let prime = vec MAX

   sieve(prime, MAX)
   
   for i=2 to MAX if i!prime
   $(  let sq = i-1
       if square(sq) then writef("%N ",sq)
   $)
   wrch('*N')

$)</lang>

Output:

1 4 16 36 100 196 256 400 576 676

C

<lang c>#include <stdio.h>

include <stdbool.h>
include <math.h>

define MAX 1000

void sieve(int n, bool *prime) {

   prime[0] = prime[1] = false;
   for (int i=2; i<=n; i++) prime[i] = true;
   for (int p=2; p*p<=n; p++) 
       if (prime[p])
           for (int c=p*p; c<=n; c+=p) prime[c] = false;

}

bool square(int n) {

   int sq = sqrt(n);
   return (sq * sq == n);

}

int main() {

   bool prime[MAX + 1];
   sieve(MAX, prime);
   for (int i=2; i<=MAX; i++) if (prime[i]) {
       int sq = i-1;
       if (square(sq)) printf("%d ", sq);
   }
   printf("\n");
   return 0;

}</lang>

Output:

1 4 16 36 100 196 256 400 576 676

CLU

<lang 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

sieve = proc (n: int) returns (array[int])

   prime: array[bool] := array[bool]$fill(2,n-1,true)
   primes: array[int] := array[int]$predict(1,isqrt(n))
   for p: int in int$from_to(2,isqrt(n)) do
       if prime[p] then
           for c: int in int$from_to_by(p*p,n,p) do
               prime[c] := false
           end
       end
   end
   for p: int in array[bool]$indexes(prime) do
       if prime[p] then array[int]$addh(primes,p) end
   end
   return(primes)

end sieve

is_square = proc (n: int) returns (bool)

   return(isqrt(n) ** 2 = n)

end is_square

start_up = proc ()

   po: stream := stream$primary_output()
   primes: array[int] := sieve(1000)
   
   for prime: int in array[int]$elements(primes) do
       n: int := prime-1
       if is_square(n) then stream$puts(po, int$unparse(n) || " ") end
   end

end start_up</lang>

Output:

1 4 16 36 100 196 256 400 576 676

COBOL

<lang cobol> IDENTIFICATION DIVISION.

      PROGRAM-ID. SQUARE-PLUS-1-PRIME.
      
      DATA DIVISION.
      WORKING-STORAGE SECTION.
      01 N                   PIC 999.
      01 P                   PIC 9999 VALUE ZERO.
      01 PRIMETEST.
         03 DSOR             PIC 9999.
         03 PRIME-FLAG       PIC X.
            88 PRIME         VALUE '*'.
         03 DIVTEST          PIC 9999V999.
         03 FILLER           REDEFINES DIVTEST.
            05 FILLER        PIC 9999.
            05 FILLER        PIC 999.
               88 DIVISIBLE  VALUE ZERO.
          
      PROCEDURE DIVISION.
      BEGIN.
          PERFORM CHECK-N VARYING N FROM 1 BY 1 
               UNTIL P IS GREATER THAN 1000.
          STOP RUN.
      
      CHECK-N.
          MULTIPLY N BY N GIVING P.
          ADD 1 TO P.
          PERFORM CHECK-PRIME.
          SUBTRACT 1 FROM P.
          IF PRIME, DISPLAY P.
          
      CHECK-PRIME.
          IF P IS LESS THAN 2, MOVE SPACE TO PRIME-FLAG,
          ELSE, MOVE '*' TO PRIME-FLAG.
          PERFORM CHECK-DSOR VARYING DSOR FROM 2 BY 1
              UNTIL NOT PRIME OR DSOR IS GREATER THAN N.
      
      CHECK-DSOR.
          DIVIDE P BY DSOR GIVING DIVTEST.
          IF DIVISIBLE, MOVE SPACE TO PRIME-FLAG.</lang>

Output:

Cowgol

<lang cowgol>include "cowgol.coh";

const MAX := 1000;

sub isqrt(s: uint16): (x0: uint16) is

   x0 := s>>1;
   if x0 == 0 then
       x0 := s;
   else
       loop
           var x1: uint16 := (x0 + s/x0) >> 1;
           if x1 >= x0 then return; end if;
           x0 := x1;
       end loop;
   end if;

end sub;

var prime: uint8[MAX + 1]; MemSet(&prime[0], 1, @bytesof prime);

var p: uint16 := 2; while p*p <= MAX loop

   if prime[p] != 0 then
       var c := p*p;
       while c <= MAX loop
           prime[c] := 0;
           c := c + p;
       end loop;
   end if;
   p := p + 1;

end loop;

var i: uint16 := 2; while i <= MAX loop

   if prime[i] != 0 then
       var sq := i - 1;
       var sqr := isqrt(sq);
       if sqr*sqr == sq then
           print_i16(sq);
           print_nl();
       end if;
   end if;
   i := i + 1;

end loop;</lang>

Output:

F#

This task uses Extensible Prime Generator (F#) <lang fsharp> // Find squares n where n+1 is prime. Nigel Galloway: December 17th., 2021 seq{yield 1; for g in 2..2..30 do let n=g*g in if isPrime(n+1) then yield n}|>Seq.iter(printf "%d "); printfn "" </lang>

Output:

1 4 16 36 100 196 256 400 576 676

Fermat

<lang fermat>!!1; i:=2; i2:=4; while i2<1000 do

   if Isprime(i2+1) then !!i2 fi;
   i:+2;
   i2:=i^2;

od;</lang>

Output:

1

4 16 36 100 196 256 400 576 676

FreeBASIC

<lang freebasic>function isprime(n as integer) as boolean

   if n<0 then return isprime(-n)
   if n<2 then return false
   if n<4 then return true
   dim as uinteger i=3
   while i*i<n
       if n mod i = 0 then return false
       i+=2
   wend
   return true

end function

print 1;" "; dim as integer n=2, n2=4 while n2<1000

   if isprime(1+n2) then print n2;"  ";
   n+=2
   n2=n^2

wend</lang>

Output:

 1   4   16   36   100   196   256   400   576   676

Go

Translation of: Wren

Library: Go-rcu

<lang go>package main

import (

   "fmt"
   "math"
   "rcu"

)

func main() {

   var squares []int
   limit := int(math.Sqrt(1000))
   i := 1
   for i <= limit {
       n := i * i
       if rcu.IsPrime(n + 1) {
           squares = append(squares, n)
       }
       if i == 1 {
           i = 2
       } else {
           i += 2
       }
   }
   fmt.Println("There are", len(squares), "square numbers 'n' where 'n+1' is prime, viz:")
   fmt.Println(squares)

}</lang>

Output:

There are 10 square numbers 'n' where 'n+1' is prime, viz:
[1 4 16 36 100 196 256 400 576 676]

GW-BASIC

<lang gwbasic>10 PRINT 1 20 N = 2 : N2 = 4 30 WHILE N2 < 1000 40 J = N2+1 50 GOSUB 110 60 IF PRIME = 1 THEN PRINT N2 70 N = N + 2 80 N2 = N*N 90 WEND 100 END 110 PRIME = 0 120 IF J < 2 THEN RETURN 130 PRIME = 1 140 IF J<4 THEN RETURN 150 I=5 160 WHILE I*I<J 170 IF J MOD I = 0 THEN PRIME = 0 : RETURN 180 I=I +2 190 WEND 200 RETURN</lang>

Output:

1

4 16 36 100 196 256 400 576 676

J

Output:

1 4 16 36 100 196 256 400 576 676

jq

Works with: jq

Works with gojq, the Go implementation of jq

See Erdős-primes#jq for a suitable definition of `is_prime` as used here.

<lang jq>def squares_for_which_successor_is_prime:

 (. // infinite) as $limit
 | {i:1, sq: 1}
 | while( .sq < $limit; .i += 1 | .sq = .i*.i)
 | .sq
 | select((. + 1)|is_prime) ;

1000 | squares_for_which_successor_is_prime</lang>

Output:

Julia

<lang julia>using Primes

isintegersquarebeforeprime(n) = isqrt(n)^2 == n && isprime(n + 1)

foreach(p -> print(lpad(last(p), 5)), filter(isintegersquarebeforeprime, 1:1000))

</lang>

Output:

    1    4   16   36  100  196  256  400  576  676

MAD

<lang MAD> NORMAL MODE IS INTEGER

           BOOLEAN PRIME
           DIMENSION PRIME(1000)
           
           INTERNAL FUNCTION(S)
           ENTRY TO ISQRT.
           X0 = S/2
           WHENEVER X0.E.0, FUNCTION RETURN S

FNDRT X1 = (X0 + S/X0)/2

           WHENEVER X1.GE.X0, FUNCTION RETURN X0
           X0 = X1
           TRANSFER TO FNDRT
           END OF FUNCTION
           
           THROUGH INIT, FOR P=2, 1, P.G.1000

INIT PRIME(P) = 1B

           THROUGH SIEVE, FOR P=2, 1, P*P.G.1000
           THROUGH SIEVE, FOR C=P*P, P, C.G.1000

SIEVE PRIME(C) = 0B

           THROUGH TEST, FOR P=2, 1, P.G.1000
           WHENEVER PRIME(P)
               SQ = P-1
               SQR = ISQRT.(SQ)
               WHENEVER SQR*SQR.E.SQ
                   PRINT FORMAT FMT, SQ
               END OF CONDITIONAL
           END OF CONDITIONAL

TEST CONTINUE

           VECTOR VALUES FMT = $I4*$
           END OF PROGRAM</lang>

Output:

Mathematica / Wolfram Language

<lang Mathematica>Cases[Table[n^2, {n, 101}], _?(PrimeQ[# + 1] &)]</lang>

Output:

{1,4,16,36,100,196,256,400,576,676,1296,1600,2916,3136,4356,5476,7056,8100,8836}

Modula-2

<lang modula2>MODULE SquareAlmostPrime; FROM InOut IMPORT WriteCard, WriteLn; FROM MathLib IMPORT sqrt;

CONST Max = 1000;

VAR prime: ARRAY [0..Max] OF BOOLEAN;

   i, sq: CARDINAL;

PROCEDURE Sieve;

   VAR i, j, sqmax: CARDINAL;

BEGIN

   sqmax := TRUNC(sqrt(FLOAT(Max)));
   FOR i := 2 TO Max DO prime[i] := TRUE; END;
   FOR i := 2 TO sqmax DO
       IF prime[i] THEN
           j := i * i;
           WHILE j <= Max DO
               prime[j] := FALSE;
               j := j + i;
           END;
       END;
   END;

END Sieve;

PROCEDURE isSquare(n: CARDINAL): BOOLEAN;

   VAR sq: CARDINAL;

BEGIN

   sq := TRUNC(sqrt(FLOAT(n)));
   RETURN sq * sq = n;

END isSquare;

BEGIN

   Sieve;
   FOR i := 2 TO Max DO
       IF prime[i] THEN
           sq := i-1;
           IF isSquare(sq) THEN
               WriteCard(sq, 4);
               WriteLn;
           END;
       END;
   END;

END SquareAlmostPrime.</lang>

Output:

PARI/GP

This is not terribly efficient, but it does show off the issquare and isprime functions.

<lang parigp>for(n = 1, 1000, if(issquare(n)&&isprime(n+1),print(n)))</lang>

Output:

1

4 16 36 100 196 256 400 576

676

Perl

Simple and Clear

<lang perl>#!/usr/bin/perl use strict; # https://rosettacode.org/wiki/Find_squares_n_where_n%2B1_is_prime use warnings; use ntheory qw( primes is_square );

my @answer = grep is_square($_), map $_ - 1, @{ primes(1000) }; print "@answer\n";</lang>

Output:

1 4 16 36 100 196 256 400 576 676

More Than One Way

TMTOWTDI, right? So do it. <lang perl>use strict; use warnings; use feature 'say'; use ntheory 'is_prime';

my $a; is_prime $_ and $a = sqrt $_-1 and $a == int $a and say $_-1 for 1..1000; # backwards approach my $b; do { say $b**2 if is_prime 1 + ++$b**2 } until $b > int sqrt 1000; # do/until my $c; while (++$c < int sqrt 1000) { say $c**2 if is_prime 1 + $c**2 } # while/if say for map $_**2, grep is_prime 1 + $_**2, 1 .. int sqrt 1000; # for/map/grep for (1 .. int sqrt 1000) { say $_**2 if is_prime 1 + $_**2 } # for/if say $_**2 for grep is_prime 1 + $_**2, 1 .. int sqrt 1000; # for/grep is_prime 1 + $_**2 and say $_**2 for 1 .. int sqrt 1000; # and/for is_prime 1+$_**2&&say$_**2for 1..31; # and/for golf, FTW

or dispense with the module and find primes the slowest way possible

(1 x (1+$_**2)) !~ /^(11+)\1+$/ and say $_**2 for 1 .. int sqrt 1000;</lang>

Output:

In all cases:

Phix

with javascript_semantics
sequence res = {1}
integer sq = 4, d = 2
while sq<1000 do
    if is_prime(sq+1) then
        res &= sq
    end if
    d += 4
    sq += 2*d
end while
printf(1,"%V\n",{res})

Output:

{1,4,16,36,100,196,256,400,576,676}

Alternative, same output, but 168 iterations/tests compared to just 16 by the above:

with javascript_semantics
function sq(integer n) return integer(sqrt(n)) end function
pp(filter(sq_sub(get_primes_le(1000),1),sq))

Drop the filter to get the 168 (cheekily humorous) squares-of-integers-and-non-integers result of Raku (and format/arrange them identically):

puts(1,join_by(apply(true,sprintf,{{"%3d"},sq_sub(get_primes_le(1000),1)}),1,20," "))

Python

<lang python> limit = 1000 print("working...")

def isprime(n):

   for i in range(2,int(n**0.5)+1):
       if n%i==0:
           return False
   return True

def issquare(x): for n in range(1,x+1): if (x == n*n): return 1 return 0

for n in range(limit-1): if issquare(n) and isprime(n+1): print(n,end=" ")

print() print("done...") </lang>

Output:

working...
1 4 16 36 100 196 256 400 576 676 
done...

Raku

Use up to to one thousand (1,000) rather than up to one (1.000) as otherwise it would be a pretty short list... <lang perl6>say ({$++²}…^*>Ⅿ).grep: (*+1).is-prime</lang>

Output:

(1 4 16 36 100 196 256 400 576 676)

Although, technically, there is absolutely nothing in the task directions specifying that n needs to be the square of an integer. So, more accurately... <lang perl6>put (^Ⅿ).grep(*.is-prime).map(*-1).batch(20)».fmt("%3d").join: "\n"</lang>

Output:

  1   2   4   6  10  12  16  18  22  28  30  36  40  42  46  52  58  60  66  70
 72  78  82  88  96 100 102 106 108 112 126 130 136 138 148 150 156 162 166 172
178 180 190 192 196 198 210 222 226 228 232 238 240 250 256 262 268 270 276 280
282 292 306 310 312 316 330 336 346 348 352 358 366 372 378 382 388 396 400 408
418 420 430 432 438 442 448 456 460 462 466 478 486 490 498 502 508 520 522 540
546 556 562 568 570 576 586 592 598 600 606 612 616 618 630 640 642 646 652 658
660 672 676 682 690 700 708 718 726 732 738 742 750 756 760 768 772 786 796 808
810 820 822 826 828 838 852 856 858 862 876 880 882 886 906 910 918 928 936 940
946 952 966 970 976 982 990 996

Ring

<lang ring> load "stdlib.ring" row = 0 limit = 1000 see "working..." + nl

for n = 1 to limit-1

   if issquare(n) and isprime(n+1)
      row++
      see "" + n +nl
   ok

func issquare(x)

    for n = 1 to sqrt(x)
        if x = pow(n,2)
           return 1
        ok
    next
    return 0

</lang>

Output:

working...
1
4
16
36
100
196
256
400
576
676
Found 10 numbers
done...

Sidef

<lang ruby>1..1000.isqrt -> map { _**2 }.grep { is_prime(_+1) }.say</lang>

Output:

[1, 4, 16, 36, 100, 196, 256, 400, 576, 676]

Tiny BASIC

<lang tinybasic> PRINT 1

     LET N = 2
     LET M = 4
  10 LET J = M + 1
     GOSUB 20
     IF P = 1 THEN PRINT M
     LET N = N + 2
     LET M = N*N
     IF M < 1000 THEN GOTO 10
     END
  20 LET P = 0
     LET I = 3
  30 IF (J/I)*I = J THEN RETURN
     LET I = I + 2
     IF I*I < J THEN GOTO 30
     LET P = 1
     RETURN</lang>

Output:

1

4 16 36 100 196 256 400 576

676

Wren

Library: Wren-math

<lang ecmascript>import "./math" for Int

var squares = [] var limit = 1000.sqrt.floor var i = 1 while (i <= limit) {

   var n = i * i
   if (Int.isPrime(n+1)) squares.add(n)
   i = (i == 1) ? 2 : i + 2

} System.print("There are %(squares.count) square numbers 'n' where 'n+1' is prime, viz:") System.print(squares)</lang>

Output:

There are 10 square numbers 'n' where 'n+1' is prime, viz:
[1, 4, 16, 36, 100, 196, 256, 400, 576, 676]

XPL0

<lang XPL0>func IsPrime(N); \Return 'true' if N is prime int N, I; [if N <= 2 then return N = 2; if (N&1) = 0 then \even >2\ return false; for I:= 3 to sqrt(N) do

   [if rem(N/I) = 0 then return false;
   I:= I+1;
   ];

return true; ]; \IsPrime

int N; [for N:= 1 to sqrt(1000-1) do

   if IsPrime(N*N+1) then
       [IntOut(0, N*N);  ChOut(0, ^ )];

]</lang>

Output:

1 4 16 36 100 196 256 400 576 676