Ulam spiral (for primes)

From Rosetta Code
Task
Ulam spiral (for primes)
You are encouraged to solve this task according to the task description, using any language you may know.

An Ulam spiral (of primes numbers) is a method of visualizing prime numbers when expressed in a (normally counter-clockwise) outward spiral (usually starting at 1),   constructed on a square grid, starting at the "center".

An Ulam spiral is also known as a   prime spiral.

The first grid (green) is shown with all numbers (primes and non-primes) shown, starting at   1.

In an Ulam spiral of primes, only the primes are shown (usually indicated by some glyph such as a dot or asterisk),   and all non-primes as shown as a blank   (or some other whitespace).

Of course, the grid and border are not to be displayed (but they are displayed here when using these Wiki HTML tables).

Normally, the spiral starts in the "center",   and the   2nd   number is to the viewer's right and the number spiral starts from there in a counter-clockwise direction.

There are other geometric shapes that are used as well, including clock-wise spirals.

Also, some spirals (for the   2nd   number)   is viewed upwards from the   1st   number instead of to the right, but that is just a matter of orientation.

Sometimes, the starting number can be specified to show more visual striking patterns (of prime densities).

[A larger than necessary grid (numbers wise) is shown here to illustrate the pattern of numbers on the diagonals   (which may be used by the method to orientate the direction of spiral-construction algorithm within the example computer programs)].

Then, in the next phase in the transformation of the Ulam prime spiral,   the non-primes are translated to blanks.

In the orange grid below,   the primes are left intact,   and all non-primes are changed to blanks.

Then, in the final transformation of the Ulam spiral (the yellow grid),   translate the primes to a glyph such as a     or some other suitable glyph.

65 64 63 62 61 60 59 58 57
66 37 36 35 34 33 32 31 56
67 38 17 16 15 14 13 30 55
68 39 18 5 4 3 12 29 54
69 40 19 6 1 2 11 28 53
70 41 20 7 8 9 10 27 52
71 42 21 22 23 24 25 26 51
72 43 44 45 46 47 48 49 50
73 74 75 76 77 78 79 80 81
61 59
37 31
67 17 13
5 3 29
19 2 11 53
41 7
71 23
43 47
73 79



The Ulam spiral becomes more visually obvious as the grid increases in size.


Task

For any sized   N x N   grid,   construct and show an Ulam spiral (counter-clockwise) of primes starting at some specified initial number   (the default would be 1),   with some suitably   dotty   (glyph) representation to indicate primes,   and the absence of dots to indicate non-primes.

You should demonstrate the generator by showing at Ulam prime spiral large enough to (almost) fill your terminal screen.


Related tasks


See also



360 Assembly[edit]

Translation of: Fortran

Compacted and optimized solution.

*        Ulam spiral               26/04/2016
ULAM CSECT
USING ULAM,R13 set base register
SAVEAREA B STM-SAVEAREA(R15) skip savearea
DC 17F'0' savearea
STM STM R14,R12,12(R13) prolog
ST R13,4(R15) save previous SA
ST R15,8(R13) linkage in previous SA
LR R13,R15 establish addressability
LA R5,1 n=1
LH R8,NSIZE x=nsize
SRA R8,1
LA R8,1(R8) x=nsize/2+1
LR R9,R8 y=x
LR R1,R5 n
BAL R14,ISPRIME
C R0,=F'1' if isprime(n)
BNE NPRMJ0
BAL R14,SPIRALO spiral(x,y)=o
NPRMJ0 LA R5,1(R5) n=n+1
LA R6,1 i=1
LOOPI1 LH R2,NSIZE do i=1 to nsize-1 by 2
BCTR R2,0
CR R6,R2 if i>nsize-1
BH ELOOPI1
LR R7,R6 j=i; do j=1 to i
LOOPJ1 LA R8,1(R8) x=x+1
LR R1,R5 n
BAL R14,ISPRIME
C R0,=F'1' if isprime(n)
BNE NPRMJ1
BAL R14,SPIRALO spiral(x,y)=o
NPRMJ1 LA R5,1(R5) n=n+1
BCT R7,LOOPJ1 next j
ELOOPJ1 LR R7,R6 j=i; do j=1 to i
LOOPJ2 BCTR R9,0 y=y-1
LR R1,R5 n
BAL R14,ISPRIME
C R0,=F'1' if isprime(n)
BNE NPRMJ2
BAL R14,SPIRALO spiral(x,y)=o
NPRMJ2 LA R5,1(R5) n=n+1
BCT R7,LOOPJ2 next j
ELOOPJ2 LR R7,R6 j=i
LA R7,1(R7) j=i+1; do j=1 to i+1
LOOPJ3 BCTR R8,0 x=x-1
LR R1,R5 n
BAL R14,ISPRIME
C R0,=F'1' if isprime(n)
BNE NPRMJ3
BAL R14,SPIRALO spiral(x,y)=o
NPRMJ3 LA R5,1(R5) n=n+1
BCT R7,LOOPJ3 next j
ELOOPJ3 LR R7,R6 j=i
LA R7,1(R7) j=i+1; do j=1 to i+1
LOOPJ4 LA R9,1(R9) y=y+1
LR R1,R5 n
BAL R14,ISPRIME
C R0,=F'1' if isprime(n)
BNE NPRMJ4
BAL R14,SPIRALO spiral(x,y)=o
NPRMJ4 LA R5,1(R5) n=n+1
BCT R7,LOOPJ4 next j
ELOOPJ4 LA R6,2(R6) i=i+2
B LOOPI1
ELOOPI1 LH R7,NSIZE j=nsize
BCTR R7,0 j=nsize-1; do j=1 to nsize-1
LOOPJ5 LA R8,1(R8) x=x+1
LR R1,R5 n
BAL R14,ISPRIME
C R0,=F'1' if isprime(n)
BNE NPRMJ5
BAL R14,SPIRALO spiral(x,y)=o
NPRMJ5 LA R5,1(R5) n=n+1
BCT R7,LOOPJ5 next j
ELOOPJ5 LA R6,1 i=1
LOOPI2 CH R6,NSIZE do i=1 to nsize
BH ELOOPI2
LA R10,PG reset buffer
LA R7,1 j=1
LOOPJ6 CH R7,NSIZE do j=1 to nsize
BH ELOOPJ6
LR R1,R7 j
BCTR R1,0 (j-1)
MH R1,NSIZE (j-1)*nsize
AR R1,R6 r1=(j-1)*nsize+i
LA R14,SPIRAL-1(R1) @spiral(j,i)
MVC 0(1,R10),0(R14) output spiral(j,i)
LA R10,1(R10) pgi=pgi+1
LA R7,1(R7) j=j+1
B LOOPJ6
ELOOPJ6 XPRNT PG,80 print
LA R6,1(R6) i=i+1
B LOOPI2
ELOOPI2 L R13,4(0,R13) reset previous SA
LM R14,R12,12(R13) restore previous env
XR R15,R15 set return code
BR R14 call back
ISPRIME CNOP 0,4 ---------- isprime function
C R1,=F'2' if nn=2
BNE NOT2
LA R0,1 rr=1
B ELOOPII
NOT2 C R1,=F'2' if nn<2
BL RRZERO
LR R2,R1 nn
LA R4,2 2
SRDA R2,32 shift
DR R2,R4 nn/2
C R2,=F'0' if nn//2=0
BNE TAGII
RRZERO SR R0,R0 rr=0
B ELOOPII
TAGII LA R0,1 rr=1
LA R4,3 ii=3
LOOPII LR R3,R4 ii
MR R2,R4 ii*ii
CR R3,R1 if ii*ii<=nn
BH ELOOPII
LR R3,R1 nn
LA R2,0 clear
DR R2,R4 nn/ii
LTR R2,R2 if nn//ii=0
BNZ NEXTII
SR R0,R0 rr=0
B ELOOPII
NEXTII LA R4,2(R4) ii=ii+2
B LOOPII
ELOOPII BR R14 ---------- end isprime return rr
SPIRALO CNOP 0,4 ---------- spiralo subroutine
LR R1,R8 x
BCTR R1,0 x-1
MH R1,NSIZE (x-1)*nsize
AR R1,R9 r1=(x-1)*nsize+y
LA R10,SPIRAL-1(R1) r10=@spiral(x,y)
MVC 0(1,R10),O spiral(x,y)=o
BR R14 ---------- end spiralo
NS EQU 79 4n+1
NSIZE DC AL2(NS) =H'ns'
O DC CL1'*' if prime
PG DC CL80' ' buffer
LTORG
SPIRAL DC (NS*NS)CL1' '
YREGS
END ULAM
Output:
        *   * *   *
 *     *         *
  *   * *
         * *     *
  * *   *       *
         * *   *
*   * *     * * *
 * * * *   *
        * * *
   *   *  ** * * *
    * * *
     *   *
*   * *   *   * *
 *   *     *     *
      *           *
 * *     *   *   *
  *           *
     *   * *
    * *   *     *

Ada[edit]

This is a generic solution. It is straightforward to use it to print spirals for any kind of numbers, rather than spirals of primes, only.

The specification of package generic_ulam is as follows:

generic
Size: Positive;
-- determines the size of the square
with function Represent(N: Natural) return String;
-- this turns a number into a string to be printed
-- the length of the output should not change
-- e.g., Represent(N) may return " #" if N is a prime
-- and " " else
with procedure Put_String(S: String);
-- outputs a string, no new line
with procedure New_Line;
-- the name says all
package Generic_Ulam is
 
procedure Print_Spiral;
-- calls Put_String(Represent(I)) N^2 times
-- and New_Line N times
 
end Generic_Ulam;

Here is the implementation:

package body Generic_Ulam is
 
subtype Index is Natural range 0 .. Size-1;
subtype Number is Positive range 1 .. Size**2;
 
function Cell(Row, Column: Index) return Number is
-- outputs the number at the given position in the square
-- taken from the Python solution
X: Integer := Column - (Size-1)/2;
Y: Integer := Row - Size/2;
MX: Natural := abs(X);
MY: Natural := abs(Y);
L: Natural := 2 * Natural'Max(MX, MY);
D: Integer;
begin
if Y >= X then
D := 3 * L + X + Y;
else
D := L - X - Y;
end if;
return (L-1) ** 2 + D;
end Cell;
 
procedure Print_Spiral is
N: Number;
begin
for R in Index'Range loop
for C in Index'Range loop
N := Cell(R, C);
Put_String(Represent(N));
end loop;
New_Line;
end loop;
end Print_Spiral;
 
end Generic_Ulam;

The folowing implementation prints a 29*29 spiral with the primes represented as numbers, and a 10*10 spiral with the primes as boxes. It uses the generic function Prime_Numbers.Is_Prime, as specified in Prime decomposition#Ada.

with Generic_Ulam, Ada.Text_IO, Prime_Numbers;
 
procedure Ulam is
 
package P is new Prime_Numbers(Natural, 0, 1, 2);
 
function Vis(N: Natural) return String is
(if P.Is_Prime(N) then " <>" else " ");
 
function Num(N: Natural) return String is
(if P.Is_Prime(N) then
(if N < 10 then " " elsif N < 100 then " " else "") & Natural'Image(N)
else " ---");
 
procedure NL is
begin
Ada.Text_IO.New_Line;
end NL;
 
package Numeric is new Generic_Ulam(29, Num, Ada.Text_IO.Put, NL);
package Visual is new Generic_Ulam(10, Vis, Ada.Text_IO.Put, NL);
 
begin
Numeric.Print_Spiral;
NL;
Visual.Print_Spiral;
end Ulam;
Output:
 --- --- --- --- --- --- --- --- --- --- --- --- 773 --- --- --- 769 --- --- --- --- --- --- --- 761 --- --- --- 757
 --- 677 --- --- --- 673 --- --- --- --- --- --- --- --- --- --- --- 661 --- 659 --- --- --- --- --- 653 --- --- ---
 787 --- 577 --- --- --- --- --- 571 --- 569 --- --- --- --- --- 563 --- --- --- --- --- 557 --- --- --- --- --- ---
 --- --- --- --- --- --- --- --- --- 479 --- --- --- --- --- --- --- --- --- --- --- 467 --- --- --- 463 --- --- ---
 --- --- --- --- 401 --- --- --- 397 --- --- --- --- --- --- --- 389 --- --- --- --- --- 383 --- --- --- --- --- ---
 --- --- --- 487 --- --- --- --- --- --- --- --- --- 317 --- --- --- 313 --- 311 --- --- --- 307 --- 461 --- 647 ---
 --- --- --- --- --- --- 257 --- --- --- --- --- 251 --- --- --- --- --- --- --- --- --- 241 --- 379 --- --- --- 751
 --- 683 --- --- --- --- --- 197 --- --- --- 193 --- 191 --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
 --- --- --- --- --- --- --- --- --- --- --- --- --- --- 139 --- 137 --- --- --- --- --- 239 --- --- --- 547 --- ---
 --- --- --- 491 --- --- --- 199 --- 101 --- --- ---  97 --- --- --- --- --- --- --- 181 --- --- --- 457 --- 643 ---
 --- --- --- --- --- --- --- --- --- --- --- --- --- ---  61 ---  59 --- --- --- 131 --- --- --- --- --- --- --- ---
 --- --- --- --- --- 331 --- --- --- 103 ---  37 --- --- --- --- ---  31 ---  89 --- 179 --- --- --- --- --- 641 ---
 797 --- 587 --- 409 --- 263 --- 149 ---  67 ---  17 --- --- ---  13 --- --- --- --- --- --- --- 373 --- --- --- ---
 --- --- --- --- --- --- --- --- --- --- --- --- ---   5 ---   3 ---  29 --- --- --- --- --- --- --- --- --- --- ---
 --- --- --- --- --- --- --- --- 151 --- --- ---  19 --- ---   2  11 ---  53 --- 127 --- 233 --- --- --- 541 --- 743
 --- 691 --- --- --- --- --- --- --- 107 ---  41 ---   7 --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
 --- --- --- --- --- --- --- --- --- ---  71 --- --- ---  23 --- --- --- --- --- --- --- --- --- --- --- --- --- ---
 --- --- --- 499 --- 337 --- --- --- 109 ---  43 --- --- ---  47 --- --- ---  83 --- 173 --- --- --- 449 --- --- ---
 --- --- 593 --- --- --- 269 --- --- ---  73 --- --- --- --- ---  79 --- --- --- --- --- 229 --- 367 --- --- --- 739
 --- --- --- --- --- --- --- --- --- --- --- 113 --- --- --- --- --- --- --- --- --- --- --- 293 --- --- --- --- ---
 --- --- --- --- --- --- 271 --- 157 --- --- --- --- --- 163 --- --- --- 167 --- --- --- 227 --- --- --- --- --- ---
 --- --- --- 503 --- --- --- 211 --- --- --- --- --- --- --- --- --- --- --- 223 --- --- --- --- --- --- --- 631 ---
 --- --- --- --- 419 --- --- --- --- --- 277 --- --- --- 281 --- 283 --- --- --- --- --- --- --- --- --- --- --- ---
 --- --- --- --- --- --- --- --- --- 347 --- 349 --- --- --- 353 --- --- --- --- --- 359 --- --- --- 443 --- --- ---
 809 --- 599 --- 421 --- --- --- --- --- --- --- --- --- 431 --- 433 --- --- --- --- --- 439 --- --- --- --- --- 733
 --- 701 --- --- --- 509 --- --- --- --- --- --- --- --- --- --- --- 521 --- 523 --- --- --- --- --- --- --- --- ---
 811 --- 601 --- --- --- --- --- 607 --- --- --- --- --- 613 --- --- --- 617 --- 619 --- --- --- --- --- --- --- ---
 --- --- --- --- --- --- --- 709 --- --- --- --- --- --- --- --- --- 719 --- --- --- --- --- --- --- 727 --- --- ---
 --- --- --- --- --- --- --- --- 821 --- 823 --- --- --- 827 --- 829 --- --- --- --- --- --- --- --- --- 839 --- ---

          <>                  
             <>    <>         
    <>                <>    <>
 <>    <>          <>         
          <>    <>    <>      
       <>       <> <>    <>   
    <>    <>                  
 <>          <>               
    <>          <>          <>
 <>                <>         

C[edit]

 
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <math.h>
 
typedef uint32_t bitsieve;
 
unsigned sieve_check(bitsieve *b, const unsigned v)
{
if ((v != 2 && !(v & 1)) || (v < 2))
return 0;
else
return !(b[v >> 6] & (1 << (v >> 1 & 31)));
}
 
bitsieve* sieve(const unsigned v)
{
unsigned i, j;
bitsieve *b = calloc((v >> 6) + 1, sizeof(uint32_t));
 
for (i = 3; i <= sqrt(v); i += 2)
if (!(b[i >> 6] & (1 << (i >> 1 & 31))))
for (j = i*i; j < v; j += (i << 1))
b[j >> 6] |= (1 << (j >> 1 & 31));
 
return b;
}
 
#define max(x,y) ((x) > (y) ? (x) : (y))
 
/* This mapping taken from python solution */
int ulam_get_map(int x, int y, int n)
{
x -= (n - 1) / 2;
y -= n / 2;
 
int mx = abs(x), my = abs(y);
int l = 2 * max(mx, my);
int d = y > x ? l * 3 + x + y : l - x - y;
 
return pow(l - 1, 2) + d;
}
 
/* Passing a value of 0 as glyph will print numbers */
void output_ulam_spiral(int n, const char glyph)
{
/* An even side length does not make sense, use greatest odd value < n */
n -= n % 2 == 0 ? 1 : 0;
 
const char *spaces = ".................";
int mwidth = log10(n * n) + 1;
 
bitsieve *b = sieve(n * n + 1);
int x, y;
 
for (x = 0; x < n; ++x) {
for (y = 0; y < n; ++y) {
int z = ulam_get_map(y, x, n);
 
if (glyph == 0) {
if (sieve_check(b, z))
printf("%*d ", mwidth, z);
else
printf("%.*s ", mwidth, spaces);
}
else {
printf("%c", sieve_check(b, z) ? glyph : spaces[0]);
}
}
printf("\n");
}
 
free(b);
}
 
int main(int argc, char *argv[])
{
const int n = argc < 2 ? 9 : atoi(argv[1]);
 
output_ulam_spiral(n, 0);
printf("\n");
 
output_ulam_spiral(n, '#');
printf("\n");
 
return 0;
}
 
Output:

Run with a side-length of 29

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

............#...#.......#...#
.#...#...........#.#.....#...
#.#.....#.#.....#.....#......
.........#...........#...#...
....#...#.......#.....#......
...#.........#...#.#...#.#.#.
......#.....#.........#.#...#
.#.....#...#.#...............
..............#.#.....#...#..
...#...#.#...#.......#...#.#.
..............#.#...#........
.....#...#.#.....#.#.#.....#.
#.#.#.#.#.#.#...#.......#....
.............#.#.#...........
........#...#..##.#.#.#...#.#
.#.......#.#.#...............
..........#...#..............
...#.#...#.#...#...#.#...#...
..#...#...#.....#.....#.#...#
...........#...........#.....
......#.#.....#...#...#......
...#...#...........#.......#.
....#.....#...#.#............
.........#.#...#.....#...#...
#.#.#.........#.#.....#.....#
.#...#...........#.#.........
#.#.....#.....#...#.#........
.......#.........#.......#...
........#.#...#.#.........#..

The following shows a spiral that's not necessarily square, which has questionable merit:

#include <stdio.h>
#include <stdlib.h>
 
int isprime(int n)
{
int p;
for (p = 2; p*p <= n; p++)
if (n%p == 0) return 0;
return n > 2;
}
 
int spiral(int w, int h, int x, int y)
{
return y ? w + spiral(h - 1, w, y - 1, w - x - 1) : x;
}
 
int main(int c, char **v)
{
int i, j, w = 50, h = 50, s = 1;
if (c > 1 && (w = atoi(v[1])) <= 0) w = 50;
if (c > 2 && (h = atoi(v[2])) <= 0) h = w;
if (c > 3 && (s = atoi(v[3])) <= 0) s = 1;
 
for (i = 0; i < h; i++) {
for (j = 0; j < w; j++)
putchar(isprime(w*h + s - 1 - spiral(w, h, j, i))[" #"]);
putchar('\n');
}
return 0;
}

C++[edit]

parametric version[edit]

#include <cmath>
#include <iostream>
#include <string>
#include <iomanip>
#include <vector>
 
class ulamSpiral {
public:
void create( unsigned n, unsigned startWith = 1 ) {
_lst.clear();
if( !( n & 1 ) ) n++;
_mx = n;
unsigned v = n * n;
_wd = static_cast<unsigned>( log10( static_cast<long double>( v ) ) ) + 1;
for( unsigned u = 0; u < v; u++ )
_lst.push_back( -1 );
 
arrange( startWith );
 
}
void display( char c ) {
if( !c ) displayNumbers();
else displaySymbol( c );
}
 
private:
bool isPrime( unsigned u ) {
if( u < 4 ) return u > 1;
if( !( u % 2 ) || !( u % 3 ) ) return false;
 
unsigned q = static_cast<unsigned>( sqrt( static_cast<long double>( u ) ) ),
c = 5;
while( c <= q ) {
if( !( u % c ) || !( u % ( c + 2 ) ) ) return false;
c += 6;
}
return true;
}
void arrange( unsigned s ) {
unsigned stp = 1, n = 1, posX = _mx >> 1,
posY = posX, stC = 0;
int dx = 1, dy = 0;
 
while( posX < _mx && posY < _mx ) {
_lst.at( posX + posY * _mx ) = isPrime( s ) ? s : 0;
s++;
 
if( dx ) {
posX += dx;
if( ++stC == stp ) {
dy = -dx;
dx = stC = 0;
}
} else {
posY += dy;
if( ++stC == stp ) {
dx = dy;
dy = stC = 0;
stp++;
}
}
}
}
void displayNumbers() {
unsigned ct = 0;
for( std::vector<unsigned>::iterator i = _lst.begin(); i != _lst.end(); i++ ) {
if( *i ) std::cout << std::setw( _wd ) << *i << " ";
else std::cout << std::string( _wd, '*' ) << " ";
if( ++ct >= _mx ) {
std::cout << "\n";
ct = 0;
}
}
std::cout << "\n\n";
}
void displaySymbol( char c ) {
unsigned ct = 0;
for( std::vector<unsigned>::iterator i = _lst.begin(); i != _lst.end(); i++ ) {
if( *i ) std::cout << c;
else std::cout << " ";
if( ++ct >= _mx ) {
std::cout << "\n";
ct = 0;
}
}
std::cout << "\n\n";
}
 
std::vector<unsigned> _lst;
unsigned _mx, _wd;
};
 
int main( int argc, char* argv[] )
{
ulamSpiral ulam;
ulam.create( 9 );
ulam.display( 0 );
ulam.create( 35 );
ulam.display( '#' );
return 0;
}
Output:
** ** ** ** 61 ** 59 ** **
** 37 ** ** ** ** ** 31 **
67 ** 17 ** ** ** 13 ** **
** ** **  5 **  3 ** 29 **
** ** 19 ** **  2 11 ** 53
** 41 **  7 ** ** ** ** **
71 ** ** ** 23 ** ** ** **
** 43 ** ** ** 47 ** ** **
73 ** ** ** ** ** 79 ** **


    # #                     #     #
     # #     #   #           #
                #   # #   #
               #   #       #   # #
    #   #           # #     #
   # #     # #     #     #
#           #           #   #     #
 #     #   #       #     #
  #   #         #   # #   # # #
 #       #     #         # #   #
    #     #   # #               #
                 # #     #   #   #
  #   #   # #   #       #   # #
                 # #   #
#       #   # #     # # #     # # #
 # # # # # # # #   #       #
                # # #           #
           #   #  ## # # #   # # #
    #       # # #
             #   #
  #   # #   # #   #   # #   #   # #
     #   #   #     #     # #   #
              #           #
         # #     #   #   #       #
#     #   #           #       #
 #     #     #   # #
            # #   #     #   #     #
 # # # #         # #     #     # #
    #   #           # #
   # #     #     #   # #
# #       #         #       #     #
           # #   # #         #
        #   #     #     #         #
     # #     #                 #
  #       #           #   #     #

generic version[edit]

ulam.hpp

#pragma once
 
#include <cmath>
#include <sstream>
#include <iomanip>
 
inline bool is_prime(unsigned a) {
if (a == 2) return true;
if (a <= 1 || a % 2 == 0) return false;
const unsigned max(std::sqrt(a));
for (unsigned n = 3; n <= max; n += 2) if (a % n == 0) return false;
return true;
}
 
enum direction { RIGHT, UP, LEFT, DOWN };
const char* N = " ---";
 
template<const unsigned SIZE>
class Ulam
{
public:
Ulam(unsigned start = 1, const char c = '\0') {
direction dir = RIGHT;
unsigned y = SIZE / 2;
unsigned x = SIZE % 2 == 0 ? y - 1 : y; // shift left for even n's
for (unsigned j = start; j <= SIZE * SIZE - 1 + start; j++) {
if (is_prime(j)) {
std::ostringstream os("");
if (c == '\0') os << std::setw(4) << j;
else os << " " << c << ' ';
s[y][x] = os.str();
}
else s[y][x] = N;
 
switch (dir) {
case RIGHT : if (x <= SIZE - 1 && s[y - 1][x].empty() && j > start) { dir = UP; }; break;
case UP : if (s[y][x - 1].empty()) { dir = LEFT; }; break;
case LEFT : if (x == 0 || s[y + 1][x].empty()) { dir = DOWN; }; break;
case DOWN : if (s[y][x + 1].empty()) { dir = RIGHT; }; break;
}
 
switch (dir) {
case RIGHT : x += 1; break;
case UP : y -= 1; break;
case LEFT : x -= 1; break;
case DOWN : y += 1; break;
}
}
}
 
template<const unsigned S> friend std::ostream& operator <<(std::ostream&, const Ulam<S>&);
 
private:
std::string s[SIZE][SIZE];
};
 
template<const unsigned SIZE>
std::ostream& operator <<(std::ostream& os, const Ulam<SIZE>& u) {
for (unsigned i = 0; i < SIZE; i++) {
os << '[';
for (unsigned j = 0; j < SIZE; j++) os << u.s[i][j];
os << ']' << std::endl;
}
return os;
}

ulam.cpp

#include <cstdlib>
#include <iostream>
#include "ulam.hpp"
 
int main(const int argc, const char* argv[]) {
using namespace std;
 
cout << Ulam<9>() << endl;
const Ulam<9> v(1, '*');
cout << v << endl;
 
return EXIT_SUCCESS;
}
Output:
[ --- --- --- ---  61 ---  59 --- ---]
[ ---  37 --- --- --- --- ---  31 ---]
[  67 ---  17 --- --- ---  13 --- ---]
[ --- --- ---   5 ---   3 ---  29 ---]
[ --- ---  19 --- ---   2  11 ---  53]
[ ---  41 ---   7 --- --- --- --- ---]
[  71 --- --- ---  23 --- --- --- ---]
[ ---  43 --- --- ---  47 --- --- ---]
[  73 --- --- --- --- ---  79 --- ---]

[ --- --- --- ---  *  ---  *  --- ---]
[ ---  *  --- --- --- --- ---  *  ---]
[  *  ---  *  --- --- ---  *  --- ---]
[ --- --- ---  *  ---  *  ---  *  ---]
[ --- ---  *  --- ---  *   *  ---  * ]
[ ---  *  ---  *  --- --- --- --- ---]
[  *  --- --- ---  *  --- --- --- ---]
[ ---  *  --- --- ---  *  --- --- ---]
[  *  --- --- --- --- ---  *  --- ---]

D[edit]

Translation of: python
import std.stdio, std.math, std.algorithm, std.array, std.range;
 
int cell(in int n, int x, int y, in int start=1) pure nothrow @safe @nogc {
x = x - (n - 1) / 2;
y = y - n / 2;
immutable l = 2 * max(x.abs, y.abs);
immutable d = (y > x) ? (l * 3 + x + y) : (l - x - y);
return (l - 1) ^^ 2 + d + start - 1;
}
 
void showSpiral(in int n, in string symbol="# ", in int start=1, string space=null) /*@safe*/ {
if (space is null)
space = " ".replicate(symbol.length);
 
immutable top = start + n ^^ 2 + 1;
auto isPrime = [false, false, true] ~ [true, false].replicate(top / 2);
foreach (immutable x; 3 .. 1 + cast(int)real(top).sqrt) {
if (!isPrime[x])
continue;
foreach (immutable i; iota(x ^^ 2, top, x * 2))
isPrime[i] = false;
}
 
string cellStr(in int x) pure nothrow @safe @nogc {
return isPrime[x] ? symbol : space;
}
 
foreach (immutable y; 0 .. n)
n.iota.map!(x => cell(n, x, y, start)).map!cellStr.joiner.writeln;
}
 
void main() {
35.showSpiral;
}
Output:
        #   #                                           #           # 
          #   #           #       #                       #           
                                #       #   #       #                 
                              #       #               #       #   #   
        #       #                       #   #           #             
      #   #           #   #           #           #                   
#                       #                       #       #           # 
  #           #       #               #           #                   
    #       #                   #       #   #       #   #   #         
  #               #           #                   #   #       #       
        #           #       #   #                               #     
                                  #   #           #       #       #   
    #       #       #   #       #               #       #   #         
                                  #   #       #                       
#               #       #   #           #   #   #           #   #   # 
  #   #   #   #   #   #   #   #       #               #               
                                #   #   #                       #     
                      #       #     # #   #   #   #       #   #   #   
        #               #   #   #                                     
                          #       #                                   
    #       #   #       #   #       #       #   #       #       #   # 
          #       #       #           #           #   #       #       
                            #                       #                 
                  #   #           #       #       #               #   
#           #       #                       #               #         
  #           #           #       #   #                               
                        #   #       #           #       #           # 
  #   #   #   #                   #   #           #           #   #   
        #       #                       #   #                         
      #   #           #           #       #   #                       
#   #               #                   #               #           # 
                      #   #       #   #                   #           
                #       #           #           #                   # 
          #   #           #                                   #       
    #               #                       #       #           #     

Alternative Version[edit]

This generates a PGM image, using the module from the Grayscale Image Task;

import std.stdio, std.math, std.algorithm, std.array, grayscale_image;
 
uint cell(in uint n, int x, int y, in uint start=1) pure nothrow @safe @nogc {
x = x - (n - 1) / 2;
y = y - n / 2;
immutable l = 2 * max(x.abs, y.abs);
immutable d = (y > x) ? (l * 3 + x + y) : (l - x - y);
return (l - 1) ^^ 2 + d + start - 1;
}
 
bool[] primes(in uint n, in uint top, in uint start=1) pure nothrow @safe {
auto isPrime = [false, false, true] ~ [true, false].replicate(top / 2);
 
foreach (immutable x; 3 .. 1 + cast(uint)real(top).sqrt)
if (isPrime[x])
for (uint i = x ^^ 2; i < top; i += x * 2)
isPrime[i] = false;
return isPrime;
}
 
void main() {
enum n = 512;
enum start = 1;
immutable top = start + n ^^ 2 + 1;
immutable isPrime = primes(n, top, start);
auto img = new Image!Gray(n, n);
 
foreach (immutable y; 0 .. n)
foreach (immutable x; 0 .. n)
img[x, y] = isPrime[cell(n, x, y, start)] ? Gray.black : Gray.white;
 
img.savePGM("ulam_spiral.pgm");
}

EchoLisp[edit]

The plot libray includes a plot-spiral function. The nice result is here : EchoLisp Ulam spiral .

 
(lib 'plot)
 
(define *red* (rgb 1 0 0))
(define (ulam n nmax) (if ( prime? n) *red* (gray (// n nmax))))
(plot-spiral ulam 1000) ;; range [0...1000]
 

Elixir[edit]

Translation of: Ruby
defmodule Ulam do
defp cell(n, x, y, start) do
y = y - div(n, 2)
x = x - div(n - 1, 2)
l = 2 * max(abs(x), abs(y))
d = if y >= x, do: l*3 + x + y, else: l - x - y
(l - 1)*(l - 1) + d + start - 1
end
 
def show_spiral(n, symbol\\nil, start\\1) do
IO.puts "\nN : #{n}"
if symbol==nil, do: format = "~#{length(to_char_list(start + n*n - 1))}s "
prime = prime(n*n + start)
Enum.each(0..n-1, fn y ->
Enum.each(0..n-1, fn x ->
i = cell(n, x, y, start)
if symbol do
IO.write if i in prime, do: Enum.at(symbol,0), else: Enum.at(symbol,1)
else
 :io.fwrite format, [if i in prime do to_char_list(i) else "" end]
end
end)
IO.puts ""
end)
end
 
defp prime(num), do: prime(Enum.to_list(2..num), [])
defp prime([], p), do: Enum.reverse(p)
defp prime([h|t], p), do: prime((for i <- t, rem(i,h)>0, do: i), [h|p])
end
 
Ulam.show_spiral(9)
Ulam.show_spiral(25)
Ulam.show_spiral(25, ["#"," "])
Output:
N : 9
            61    59       
   37                31    
67    17          13       
          5     3    29    
      19        2 11    53 
   41     7                
71          23             
   43          47          
73                79       

N : 25
577                     571     569                     563                     557                 
                            479                                             467             463     
        401             397                             389                     383                 
    487                                     317             313     311             307     461     
                257                     251                                     241     379         
                    197             193     191                                                     
                                                139     137                     239             547 
    491             199     101              97                             181             457     
                                                 61      59             131                         
            331             103      37                      31      89     179                     
587     409     263     149      67      17              13                             373         
                                              5       3      29                                     
                        151              19           2  11      53     127     233             541 
                            107      41       7                                                     
                                 71              23                                                 
    499     337             109      43              47              83     173             449     
593             269              73                      79                     229     367         
                                    113                                             293             
                271     157                     163             167             227                 
    503             211                                             223                             
        419                     277             281     283                                         
                            347     349             353                     359             443     
599     421                                     431     433                     439                 
            509                                             521     523                             
601                     607                     613             617     619                         

N : 25
#     # #     #     #    
       #           #   # 
  #   #       #     #    
 #         #   # #   # # 
    #     #         # #  
     #   # #             
            # #     #   #
 #   # #   #       #   # 
            # #   #      
   #   # #     # # #     
# # # # # #   #       #  
           # # #         
      #   #  ## # # #   #
       # # #             
        #   #            
 # #   # #   #   # #   # 
#   #   #     #     # #  
         #           #   
    # #     #   #   #    
 #   #           #       
  #     #   # #          
       # #   #     #   # 
# #         # #     #    
   #           # #       
#     #     #   # #      

ERRE[edit]

PROGRAM SPIRAL
 
!$INTEGER
 
CONST RIGHT=1,UP=2,LEFT=3,DOWN=4
 
!$DYNAMIC
DIM SPIRAL$[0,0]
 
PROCEDURE PRT_ULAM(N)
FOR ROW=0 TO N DO
FOR COL=0 TO N DO
PRINT(SPIRAL$[ROW,COL];)
END FOR
PRINT
END FOR
PRINT
GET(K$)
FOR ROW=0 TO N DO
FOR COL=0 TO N DO
IF VAL(SPIRAL$[ROW,COL])<>0 THEN PRINT(" * ";) ELSE PRINT(SPIRAL$[ROW,COL];) END IF
END FOR
PRINT
END FOR
END PROCEDURE
 
PROCEDURE IS_PRIME(A->RES%)
LOCAL N
IF A=2 THEN RES%=TRUE EXIT PROCEDURE END IF
IF A<=1 OR (A MOD 2=0) THEN RES%=FALSE EXIT PROCEDURE END IF
MAX=SQR(A)
FOR N=3 TO MAX STEP 2 DO
IF (A MOD N=0) THEN RES%=FALSE EXIT PROCEDURE END IF
END FOR
RES%=TRUE
END PROCEDURE
 
PROCEDURE GEN_ULAM(N,I)
DIR=RIGHT
J=I
Y=INT(N/2)
IF (N MOD 2=0) THEN X=Y-1 ELSE X=Y END IF ! shift left for even n's
WHILE J<=(N*N)-1+I DO
 
IS_PRIME(J->RES%)
IF RES% THEN SPIRAL$[Y,X]=RIGHT$(" "+STR$(J),4) ELSE SPIRAL$[Y,X]=" ---" END IF
 
CASE DIR OF
RIGHT->
IF (X<=(N-1) AND SPIRAL$[Y-1,X]="" AND J>I) THEN DIR=UP END IF
END ->
UP->
IF SPIRAL$[Y,X-1]="" THEN DIR=LEFT END IF
END ->
LEFT->
IF (X=0) OR SPIRAL$[Y+1,X]="" THEN DIR=DOWN END IF
END ->
DOWN->
IF SPIRAL$[Y,X+1]="" THEN DIR=RIGHT END IF
END ->
END CASE
 
CASE DIR OF
RIGHT-> X=X+1 END ->
UP-> Y=Y-1 END ->
LEFT-> X=X-1 END ->
DOWN-> Y=Y+1 END ->
END CASE
J=J+1
END WHILE
PRT_ULAM(N)
END PROCEDURE
 
BEGIN
N=9
 !$DIM SPIRAL$[N,N]
GEN_ULAM(N,1)
END PROGRAM
Output:
 --- --- --- ---  61 ---  59 --- ---
 ---  37 --- --- --- --- ---  31 ---
  67 ---  17 --- --- ---  13 --- ---
 --- --- ---   5 ---   3 ---  29 ---
 --- ---  19 --- ---   2  11 ---  53
 ---  41 ---   7 --- --- --- --- ---
  71 --- --- ---  23 --- --- --- ---
 ---  43 --- --- ---  47 --- --- ---
  73 --- --- --- --- ---  79 --- ---


 --- --- --- ---  *  ---  *  --- ---
 ---  *  --- --- --- --- ---  *  ---
  *  ---  *  --- --- ---  *  --- ---
 --- --- ---  *  ---  *  ---  *  ---
 --- ---  *  --- ---  *   *  ---  *
 ---  *  ---  *  --- --- --- --- ---
  *  --- --- ---  *  --- --- --- ---
 ---  *  --- --- ---  *  --- --- ---
  *  --- --- --- --- ---  *  --- ---

Fortran[edit]

Works with: Fortran version 95 and later

Only works with odd sized squares

program ulam
implicit none
 
integer, parameter :: nsize = 49
integer :: i, j, n, x, y
integer :: a(nsize*nsize) = (/ (i, i = 1, nsize*nsize) /)
character(1) :: spiral(nsize, nsize) = " "
character(2) :: sstr
character(10) :: fmt
 
n = 1
x = nsize / 2 + 1
y = x
if(isprime(a(n))) spiral(x, y) = "O"
n = n + 1
 
do i = 1, nsize-1, 2
do j = 1, i
x = x + 1
if(isprime(a(n))) spiral(x, y) = "O"
n = n + 1
end do
 
do j = 1, i
y = y - 1
if(isprime(a(n))) spiral(x, y) = "O"
n = n + 1
end do
 
do j = 1, i+1
x = x - 1
if(isprime(a(n))) spiral(x, y) = "O"
n = n + 1
end do
 
do j = 1, i+1
y = y + 1
if(isprime(a(n))) spiral(x, y) = "O"
n = n + 1
end do
end do
 
do j = 1, nsize-1
x = x + 1
if(isprime(a(n))) spiral(x, y) = "O"
n = n + 1
end do
 
write(sstr, "(i0)") nsize
fmt = "(" // sstr // "(a,1x))"
do i = 1, nsize
write(*, fmt) spiral(:, i)
end do
 
contains
 
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
end program

Output:

                O       O           O           O               O       O   O
          O   O                       O                   O   O       O   O
            O   O                                   O           O           O
                  O           O           O           O               O                   O   O
O       O       O                           O       O               O       O
                      O           O       O   O       O                           O       O
O           O           O   O           O       O   O                                   O   O   O
          O           O   O                                           O           O
                        O   O           O       O                       O           O
                                              O       O   O       O                           O
        O   O                               O       O               O       O   O
          O           O       O                       O   O           O
        O   O       O   O           O   O           O           O                       O
  O       O   O                       O                       O       O           O   O
    O           O           O       O               O           O                               O
  O   O           O       O                   O       O   O       O   O   O
    O   O   O   O               O           O                   O   O       O           O   O
                      O           O       O   O                               O           O
                                                O   O           O       O       O   O       O   O
          O       O       O       O   O       O               O       O   O                   O
                                                O   O       O                                   O
  O   O       O               O       O   O           O   O   O           O   O   O
        O       O   O   O   O   O   O   O   O       O               O                   O   O
                                              O   O   O                       O
        O                           O       O     O O   O   O   O       O   O   O           O
  O   O               O               O   O   O
                                        O       O
  O   O           O       O   O       O   O       O       O   O       O       O   O       O
O           O           O       O       O           O           O   O       O               O
                                          O                       O                       O
        O   O                   O   O           O       O       O               O   O
          O   O           O       O                       O               O           O
                O           O           O       O   O
                                      O   O       O           O       O           O       O   O
O               O   O   O   O                   O   O           O           O   O       O   O
                      O       O                       O   O
O           O       O   O           O           O       O   O                       O           O
  O           O   O               O                   O               O           O
    O                               O   O       O   O                   O           O
      O                       O       O           O           O                   O   O
        O               O   O           O                                   O
          O       O               O                       O       O           O
O                                                                   O           O       O
          O       O   O       O           O                       O                           O
    O                                   O           O       O   O                               O
  O           O                       O               O                               O       O
O               O           O       O   O       O               O           O
                                  O                                               O       O
        O                           O           O       O   O           O       O           O

But if you can use complex numbers...[edit]

Notice that there each move comes in pairs, lengths 1,1, 2,2, 3,3, 4,4, ... with a quarter turn for each move. The order of the work area must be an odd number so that there is a definite middle element to start with and the worm fits between the bounds of the work area rather than striking one wall and leaving tiles unused.

 
SUBROUTINE ULAMSPIRAL(START,ORDER) !Idle scribbles can lead to new ideas.
Careful with phasing: each lunge's first number is the second placed along its direction.
INTEGER START !Usually 1.
INTEGER ORDER !MUST be an odd number, so there is a middle.
INTEGER L,M,N !Counters.
INTEGER STEP,LUNGE !In some direction.
COMPLEX WAY,PLACE !Just so.
CHARACTER*1 SPLOT(0:1) !Tricks for output.
PARAMETER (SPLOT = (/" ","*"/)) !Selected according to ISPRIME(n)
INTEGER TILE(ORDER,ORDER) !Work area.
WRITE (6,1) START,ORDER !Here we go.
1 FORMAT ("Ulam spiral starting with ",I0,", of order ",I0,/)
IF (MOD(ORDER,2) .NE. 1) STOP "The order must be odd!" !Otherwise, out of bounds.
M = ORDER/2 + 1 !Find the number of the middle.
PLACE = CMPLX(M,M) !Start there.
WAY = (1,0) !Thence in the +x direction.
N = START !Different start, different layout.
DO L = 1,ORDER !Advance one step, then two, then three, etc.
DO LUNGE = 1,2 !But two lunges for each length.
DO STEP = 1,L !Take the steps.
TILE(INT(REAL(PLACE)),INT(AIMAG(PLACE))) = N !This number for this square.
PLACE = PLACE + WAY !Make another step.
N = N + 1 !Count another step.
END DO !And consider making another.
IF (N .GE. ORDER**2) EXIT !Otherwise, one lunge too many!
WAY = WAY*(0,1) !Rotate a quarter-turn counter-clockwise.
END DO !And make another lunge.
END DO !Until finished.
Cast forth the numbers.
c DO L = ORDER,1,-1 !From the top of the grid to the bottom.
c WRITE (6,66) TILE(1:ORDER,L) !One row at at time.
c 66 FORMAT (666I6) !This will do for reassurance.
c END DO !Line by line.
Cast forth the splots.
DO L = ORDER,1,-1 !Just put out a marker.
WRITE (6,67) (SPLOT(ISPRIME(TILE(M,L))),M = 1,ORDER) !One line at a time.
67 FORMAT (666A1) !A single character at each position.
END DO !On to the next row.
END SUBROUTINE ULAMSPIRAL !So much for a boring lecture.
 
INTEGER FUNCTION ISPRIME(N) !Returns 0 or 1.
INTEGER N !The number.
INTEGER F,Q !Factor and quotient.
ISPRIME = 0 !The more likely outcome.
IF (N.LE.1) RETURN !Just in case the start is peculiar.
IF (N.LE.3) GO TO 2 !Oops! I forgot this!
IF (MOD(N,2).EQ.0) RETURN !Special case.
F = 1 !Now get stuck in to testing odd numbers.
1 F = F + 2 !A trial factor.
Q = N/F !The quotient.
IF (N .EQ. Q*F) RETURN !No remainder? Not a prime.
IF (Q.GT.F) GO TO 1 !Thus chug up to the square root.
2 ISPRIME = 1 !Well!
END FUNCTION ISPRIME !Simple enough.
 
PROGRAM TWIRL
CALL ULAMSPIRAL(1,49)
END
 

One could escalate to declaring function IsPrime to be PURE so that it may be used in array expressions, such as CANVAS = SPLOT(ISPRIME(TILE)) where CANVAS is an array of single characters, but that would require another large array. Trying instead to do the conversion only a line at a time in the WRITE statement as SPLOT(ISPRIME(TILE(1:ORDER,L))) failed, only one symbol per line appeared. So instead, an older-style implicit DO-loop, and the results are...

        *   *     *     *       *   * *          
     * *           *         * *   * *           
      * *                 *     *     *          
         *     *     *     *       *         * * 
*   *   *             *   *       *   *          
           *     *   * *   *             *   *   
*     *     * *     *   * *                 * * *
     *     * *                     *     *       
            * *     *   *           *     *      
                       *   * *   *             * 
    * *               *   *       *   * *        
     *     *   *           * *     *             
    * *   * *     * *     *     *           *    
 *   * *           *           *   *     * *     
  *     *     *   *       *     *               *
 * *     *   *         *   * *   * * *           
  * * * *       *     *         * *   *     * *  
           *     *   * *               *     *   
                        * *     *   *   * *   * *
     *   *   *   * *   *       *   * *         * 
                        * *   *                 *
 * *   *       *   * *     * * *     * * *       
    *   * * * * * * * *   *       *         * *  
                       * * *           *         
    *             *   *  ** * * *   * * *     *  
 * *       *       * * *                         
                    *   *                        
 * *     *   * *   * *   *   * *   *   * *   *   
*     *     *   *   *     *     * *   *       *  
                     *           *           *   
    * *         * *     *   *   *       * *      
     * *     *   *           *       *     *     
        *     *     *   * *                      
                   * *   *     *   *     *   * * 
*       * * * *         * *     *     * *   * *  
           *   *           * *                   
*     *   * *     *     *   * *           *     *
 *     * *       *         *       *     *       
  *               * *   * *         *     *      
   *           *   *     *     *         * *     
    *       * *     *                 *          
     *   *       *           *   *     *         
*                                 *     *   *    
     *   * *   *     *           *             * 
  *                 *     *   * *               *
 *     *           *       *               *   * 
*       *     *   * *   *       *     *          
                 *                       *   *   
    *             *     *   * *     *   *     *   

Bounding the display with framework symbols might help readability, but is not in the specification.

Go[edit]

Translation of: Kotlin
package main
 
import (
"math"
"fmt"
)
 
type Direction byte
 
const (
RIGHT Direction = iota
UP
LEFT
DOWN
)
 
func generate(n,i int, c byte) {
s := make([][]string, n)
for i := 0; i < n; i++ { s[i] = make([]string, n) }
dir := RIGHT
y := n / 2
var x int
if (n % 2 == 0) { x = y - 1 } else { x = y } // shift left for even n's
 
for j := i; j <= n * n - 1 + i; j++ {
if (isPrime(j)) {
if (c == 0) { s[y][x] = fmt.Sprintf("%3d", j) } else { s[y][x] = fmt.Sprintf("%2c ", c) }
} else { s[y][x] = "---" }
 
switch dir {
case RIGHT : if (x <= n - 1 && s[y - 1][x] == "" && j > i) { dir = UP }
case UP : if (s[y][x - 1] == "") { dir = LEFT }
case LEFT : if (x == 0 || s[y + 1][x] == "") { dir = DOWN }
case DOWN : if (s[y][x + 1] == "") { dir = RIGHT }
}
 
switch dir {
case RIGHT : x += 1
case UP : y -= 1
case LEFT : x -= 1
case DOWN : y += 1
}
}
 
for _, row := range s { fmt.Println(fmt.Sprintf("%v", row)) }
fmt.Println()
}
 
func isPrime(a int) bool {
if (a == 2) { return true }
if (a <= 1 || a % 2 == 0) { return false }
max := int(math.Sqrt(float64(a)))
for n := 3; n <= max; n += 2 { if (a % n == 0) { return false } }
return true
}
 
func main() {
generate(9, 1, 0) // with digits
generate(9, 1, '*') // with *
}

Haskell[edit]

Haskell encourages splitting the task into indepentend parts each having very clear functionality:

1. preparation of data: a list of numbers is mapped into the list of symbols according to primality, or any other criterion.

2. spooling the list of arbitrary data into the spiral, forming a table.

3. displaying arbitrary table at a console or graphically.

As a program the given task then formulates as following:

import Data.List
import Data.Numbers.Primes
 
ulam n representation = swirl n . map representation

Here we refference the function swirl n, which for a given (possibly infinite) list returns n whorls of a spiral.

The spiral is formed in a way we would fold a paper band: first we chop the band into pieces of increasing length, then we take necessary amount of pieces, finally we fold all pieces into the spiral, starting with the empty table by rotating it and adding pieces of data one by one:

swirl n = spool . take (2*(n-1)+1) . chop 1
 
chop n lst = let (x,(y,z)) = splitAt n <$> splitAt n lst
in x:y:chop (n+1) z
 
spool = foldl (\table piece -> piece : rotate table) [[]]
where rotate = reverse . transpose

That's it!

Textual output[edit]

Pretty printing the table of strings with given column width is simple:

showTable w = foldMap (putStrLn . foldMap pad)
where pad s = take w $ s ++ repeat ' '
Output:
λ> showTable 3 $ ulam 10 show [1..]
91 92 93 94 95 96 97 98 99 100
90 57 58 59 60 61 62 63 64 65 
89 56 31 32 33 34 35 36 37 66 
88 55 30 13 14 15 16 17 38 67 
87 54 29 12 3  4  5  18 39 68 
86 53 28 11 2  1  6  19 40 69 
85 52 27 10 9  8  7  20 41 70 
84 51 26 25 24 23 22 21 42 71 
83 50 49 48 47 46 45 44 43 72 
82 81 80 79 78 77 76 75 74 73 

λ> showTable 3 $ ulam 10 (\x -> if isPrime x then show x else " . ") [1..]
 .  .  .  .  .  . 97  .  .  . 
 .  .  . 59  . 61  .  .  .  . 
89  . 31  .  .  .  .  . 37  . 
 .  .  . 13  .  .  . 17  . 67 
 .  . 29  . 3   . 5   .  .  . 
 . 53  . 11 2   .  . 19  .  . 
 .  .  .  .  .  . 7   . 41  . 
 .  .  .  .  . 23  .  .  . 71 
83  .  .  . 47  .  .  . 43  . 
 .  .  . 79  .  .  .  .  . 73 

λ> showTable 2 $ ulam 20 (\x -> if isPrime x then "*" else "") [1..]
    *           *               *       
  *       *   *       *                 
*   *                   *           *   
                      *   *       *     
    *           *   *                   
      *               *       *   *     
        *       *   *                   
      *   *   *           *   *       * 
*               *       *   *   *   *   
              *   *   *                 
    *   *   *   * *     *       *       
                      *   *   *         
                    *       *           
      *   *       *       *   *       * 
*   *           *           *       *   
  *                       *             
    *       *       *           *   *   
          *                       *     
                *   *       *           
      *           *       *   *         

The high modularity of the program allows us easily to start from any number and to proceed with any step size:

λ> showTable 2 $ ulam 20 (\x -> if isPrime x then "*" else "") [3,5..]
      *   *             *         *     
*   * *           *         * *   *     
  *     *   *       *   *     *       * 
*     *     *     *   *     *           
    *     * *     *   * *         *     
  *               * *   * *     *   * * 
*       * *             *   *     * * * 
      *   * *     *   * *               
  *           *   * *                   
  *     *   * *   *   * * * * *         
*   * *   * *   * * * *     *     *     
                  * *   * *             
* * * * *   * *     *   *       *     * 
    * *   * *   *       *               
            *     *     * *     *     * 
* * *       * *     *   * *   * * * *   
          *     *             *   *     
        *     *   *     * *           * 
*     *     * *     *     *         *   
      *         *       *         *     

Or we can form a spiral out of arbitrary data:

λ> showTable 1 $ ulam 10 (:[]) "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse consequat lectus at massa tristique, ut vulputate arcu pretium."
assa trist
m Suspendi
 .nsectets
ttodolorus
aic rem re
 l moL s  
se,uspiiac
u tema tdo
tgnicsipin
cel tauqes

Graphical output[edit]

Simple graphical output could be done using Diagrams framework:

import Diagrams.Prelude
import Diagrams.Backend.SVG.CmdLine
 
drawTable tbl = foldl1 (===) $ map (foldl1 (|||)) tbl :: Diagram B
 
dots x = (circle 1 # if isPrime x then fc black else fc white) :: Diagram B
 
main = mainWith $ drawTable $ ulam 100 dots [1..]

J[edit]

Let's start with our implementation of spiral:

spiral =: ,~ $ [: /: }.@(2 # >:@i.@-) +/\@# <:@+: $ (, -)@(1&,)

We can get a spiral starting with 1 in the center of the square by subtracting these values from the square of our size argument:

   spiral 5
0 1 2 3 4
15 16 17 18 5
14 23 24 19 6
13 22 21 20 7
12 11 10 9 8
(*: - spiral) 5
25 24 23 22 21
10 9 8 7 20
11 2 1 6 19
12 3 4 5 18
13 14 15 16 17

Next, we want to determine which of these numbers are prime:

   (1 p: *: - spiral) 5
0 0 1 0 0
0 0 0 1 0
1 1 0 0 1
0 1 0 1 0
1 0 0 0 1

And, finally, we want to use these values to select from a pair of characters:

   (' o' {~ 1 p: *: - spiral) 5
o
o
oo o
o o
o o

If we want our spiral to start with some value other than 1, we'd add that value - 1 to our numbers right before the prime check. For this, we want a function which returns 0 when there's no left argument and one less than the left argument when it that value present. We can use : for this -- it takes two verbs, the left of which is used when no left argument is present and the right one is used when a left argument is present. (And note that in J, : is a token forming character, so we will need to leave a space to the left of : so that it does not form a different token):

   (0: :(<:@[)) ''
0
3 (0: :(<:@[)) ''
2

We also want to specify that our initial computations only respect the right argument, and we should maybe add a space after every character to get more of a square aspect ratio in typical text displays:

ulam=: 1j1 #"1 ' o' {~ 1 p: 0: :(<:@[) + *:@] - spiral@]

And here it is in action:

   ulam 16
o o
o o o
o o o
o o o o
o o o
o o o o o
o o o o
o o o
o o o o o o o
o o o
o o
o o o o o
o o o
o
o o o o
o o
9 ulam 12
o o
o o o o
o o o o
o o o
o o
o o o o o
o o
o
o o o o
o
o o o

To transform these spirals to the orientation which has recently been added as a part of the task, you could flip them horizontally (|."1) and vertically (|.)

It should also be possible to redefine the original spiral treatment in some other ways.

See also https://www.youtube.com/watch?v=dBC5vnwf6Zw for some variations on this theme (the bit about perfect squares of the count of prime factors is striking).

Java[edit]

Works with: Java version 1.5+
import java.util.Arrays;
 
public class Ulam{
enum Direction{
RIGHT, UP, LEFT, DOWN;
}
 
private static String[][] genUlam(int n){
return genUlam(n, 1);
}
 
private static String[][] genUlam(int n, int i){
String[][] spiral = new String[n][n];
Direction dir = Direction.RIGHT;
int j = i;
int y = n / 2;
int x = (n % 2 == 0) ? y - 1 : y; //shift left for even n's
while(j <= ((n * n) - 1 + i)){
spiral[y][x] = isPrime(j) ? String.format("%4d", j) : " ---";
 
switch(dir){
case RIGHT:
if(x <= (n - 1) && spiral[y - 1][x] == null && j > i) dir = Direction.UP; break;
case UP:
if(spiral[y][x - 1] == null) dir = Direction.LEFT; break;
case LEFT:
if(x == 0 || spiral[y + 1][x] == null) dir = Direction.DOWN; break;
case DOWN:
if(spiral[y][x + 1] == null) dir = Direction.RIGHT; break;
}
 
switch(dir){
case RIGHT: x++; break;
case UP: y--; break;
case LEFT: x--; break;
case DOWN: y++; break;
}
j++;
}
return spiral;
}
 
public static boolean isPrime(int a){
if(a == 2) return true;
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;
}
 
public static void main(String[] args){
String[][] ulam = genUlam(9);
for(String[] row : ulam){
System.out.println(Arrays.toString(row).replaceAll(",", ""));
}
System.out.println();
 
for(String[] row : ulam){
System.out.println(Arrays.toString(row).replaceAll("\\[\\s+\\d+", "[ * ").replaceAll("\\s+\\d+", " * ").replaceAll(",", ""));
}
}
}
Output:
[ ---  ---  ---  ---   61  ---   59  ---  ---]
[ ---   37  ---  ---  ---  ---  ---   31  ---]
[  67  ---   17  ---  ---  ---   13  ---  ---]
[ ---  ---  ---    5  ---    3  ---   29  ---]
[ ---  ---   19  ---  ---    2   11  ---   53]
[ ---   41  ---    7  ---  ---  ---  ---  ---]
[  71  ---  ---  ---   23  ---  ---  ---  ---]
[ ---   43  ---  ---  ---   47  ---  ---  ---]
[  73  ---  ---  ---  ---  ---   79  ---  ---]

[ ---  ---  ---  ---   *   ---   *   ---  ---]
[ ---   *   ---  ---  ---  ---  ---   *   ---]
[  *   ---   *   ---  ---  ---   *   ---  ---]
[ ---  ---  ---   *   ---   *   ---   *   ---]
[ ---  ---   *   ---  ---   *    *   ---   * ]
[ ---   *   ---   *   ---  ---  ---  ---  ---]
[  *   ---  ---  ---   *   ---  ---  ---  ---]
[ ---   *   ---  ---  ---   *   ---  ---  ---]
[  *   ---  ---  ---  ---  ---   *   ---  ---]

Large scale Ulam Spiral[edit]

Ulam large java.gif
Works with: Java version 8
import java.awt.*;
import javax.swing.*;
 
public class LargeUlamSpiral extends JPanel {
 
public LargeUlamSpiral() {
setPreferredSize(new Dimension(605, 605));
setBackground(Color.white);
}
 
private boolean isPrime(int n) {
if (n <= 2 || n % 2 == 0)
return n == 2;
for (int i = 3; i * i <= n; i += 2)
if (n % i == 0)
return false;
return true;
}
 
@Override
public void paintComponent(Graphics gg) {
super.paintComponent(gg);
Graphics2D g = (Graphics2D) gg;
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
 
g.setColor(getForeground());
 
double angle = 0.0;
int x = 300, y = 300, dx = 1, dy = 0;
 
for (int i = 1, step = 1, turn = 1; i < 40_000; i++) {
 
if (isPrime(i))
g.fillRect(x, y, 2, 2);
 
x += dx * 3;
y += dy * 3;
 
if (i == turn) {
 
angle += 90.0;
 
if ((dx == 0 && dy == -1) || (dx == 0 && dy == 1))
step++;
 
turn += step;
 
dx = (int) Math.cos(Math.toRadians(angle));
dy = (int) Math.sin(Math.toRadians(-angle));
}
}
}
 
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> {
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setTitle("Large Ulam Spiral");
f.setResizable(false);
f.add(new LargeUlamSpiral(), BorderLayout.CENTER);
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
});
}
}

Small scale Ulam Spiral[edit]

Ulam spiral java.gif
Works with: Java version 8
import java.awt.*;
import javax.swing.*;
 
public class UlamSpiral extends JPanel {
 
Font primeFont = new Font("Arial", Font.BOLD, 20);
Font compositeFont = new Font("Arial", Font.PLAIN, 16);
 
public UlamSpiral() {
setPreferredSize(new Dimension(640, 640));
setBackground(Color.white);
}
 
private boolean isPrime(int n) {
if (n <= 2 || n % 2 == 0)
return n == 2;
for (int i = 3; i * i <= n; i += 2)
if (n % i == 0)
return false;
return true;
}
 
@Override
public void paintComponent(Graphics gg) {
super.paintComponent(gg);
Graphics2D g = (Graphics2D) gg;
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
 
g.setStroke(new BasicStroke(2));
 
double angle = 0.0;
int x = 280, y = 330, dx = 1, dy = 0;
 
g.setColor(getForeground());
g.drawLine(x, y - 5, x + 50, y - 5);
 
for (int i = 1, step = 1, turn = 1; i < 100; i++) {
 
g.setColor(getBackground());
g.fillRect(x - 5, y - 20, 30, 30);
g.setColor(getForeground());
g.setFont(isPrime(i) ? primeFont : compositeFont);
g.drawString(String.valueOf(i), x + (i < 10 ? 4 : 0), y);
 
x += dx * 50;
y += dy * 50;
 
if (i == turn) {
angle += 90.0;
 
if ((dx == 0 && dy == -1) || (dx == 0 && dy == 1))
step++;
 
turn += step;
 
dx = (int) Math.cos(Math.toRadians(angle));
dy = (int) Math.sin(Math.toRadians(-angle));
 
g.translate(9, -5);
g.drawLine(x, y, x + dx * step * 50, y + dy * step * 50);
g.translate(-9, 5);
}
}
}
 
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> {
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setTitle("Ulam Spiral");
f.setResizable(false);
f.add(new UlamSpiral(), BorderLayout.CENTER);
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
});
}
}

Kotlin[edit]

Translation of: Java
package ulam
 
object Ulam {
fun generate(n: Int, i: Int = 1, c: Char = '*') {
require(n > 1)
val s = Array(n) { Array(n, { "" }) }
var dir = Direction.RIGHT
var y = n / 2
var x = if (n % 2 == 0) y - 1 else y // shift left for even n's
for (j in i..n * n - 1 + i) {
s[y][x] = if (isPrime(j)) if (c.isDigit()) "%4d".format(j) else " $c " else " ---"
 
when (dir) {
Direction.RIGHT -> if (x <= n - 1 && s[y - 1][x].none() && j > i) dir = Direction.UP
Direction.UP -> if (s[y][x - 1].none()) dir = Direction.LEFT
Direction.LEFT -> if (x == 0 || s[y + 1][x].none()) dir = Direction.DOWN
Direction.DOWN -> if (s[y][x + 1].none()) dir = Direction.RIGHT
}
 
when (dir) {
Direction.RIGHT -> x++
Direction.UP -> y--
Direction.LEFT -> x--
Direction.DOWN -> y++
}
}
for (row in s) println("[" + row.joinToString("") + ']')
println()
}
 
private enum class Direction { RIGHT, UP, LEFT, DOWN }
 
private fun isPrime(a: Int): Boolean {
when {
a == 2 -> return true
a <= 1 || a % 2 == 0 -> return false
else -> {
val max = Math.sqrt(a.toDouble()).toInt()
for (n in 3..max step 2)
if (a % n == 0) return false
return true
}
}
}
}
 
fun main(args: Array<String>) {
Ulam.generate(9, c = '0')
Ulam.generate(9)
}

PARI/GP[edit]

In this version function plotulamspir() was translated from VB, plus upgraded to plot/print different kind of Ulam spirals. My own plotting helper functions and string functions were used and made it possible. You can find all of them here on RosettaCode Wiki.

Output ULAMspiral1.png
Output ULAMspiral2.png
Works with: PARI/GP version 2.7.4 and above
 
\\ Ulam spiral (plotting/printing)
\\ 4/19/16 aev
plotulamspir(n,pflg=0)={
my(n=if(n%2==0,n++,n),M=matrix(n,n),x,y,xmx,ymx,cnt,dir,n2=n*n,pch,sz=#Str(n2),pch2=srepeat(" ",sz));
if(pflg<0||pflg>2,pflg=0);
print(" *** Ulam spiral: ",n,"x",n," matrix, p-flag=",pflg);
x=y=n\2+1; xmx=ymx=cnt=1; dir="R";
for(i=1,n2,
if(isprime(i), if(!insm(M,x,y), break); if(pflg==2, M[y,x]=i, M[y,x]=1));
if(dir=="R", if(xmx>0, x++;xmx--, dir="U";ymx=cnt;y--;ymx--); next);
if(dir=="U", if(ymx>0, y--;ymx--, dir="L";cnt++;xmx=cnt;x--;xmx--); next);
if(dir=="L", if(xmx>0, x--;xmx--, dir="D";ymx=cnt;y++;ymx--); next);
if(dir=="D", if(ymx>0, y++;ymx--, dir="R";cnt++;xmx=cnt;x++;xmx--); next);
);\\fend
\\Plot/Print according to the p-flag(0-real plot,1-"*",2-primes)
if(pflg==0, plotmat(M));
if(pflg==1, for(i=1,n,
for(j=1,n, if(M[i,j]==1, pch="*", pch=" ");
print1(" ",pch)); print(" ")));
if(pflg==2, for(i=1,n,
for(j=1,n, if(M[i,j]==0, pch=pch2, pch=spad(Str(M[i,j]),sz,,1));
print1(" ",pch)); print(" ")));
}
 
{\\ Executing:
plotulamspir(9,1); \\ (see output)
plotulamspir(9,2); \\ (see output)
plotulamspir(100); \\ ULAMspiral1.png
plotulamspir(200); \\ ULAMspiral2.png
}
 
Output:
> plotulamspir(9,1);
  *** Ulam spiral: 9x9 matrix, p-flag=1
  
          *   *
    *           *
  *   *       *
        *   *   *
      *     * *   *
    *   *
  *       *
    *       *
  *           *
 
> plotulamspir(9,2);
  *** Ulam spiral: 9x9 matrix, p-flag=2
 
             61    59
    37                31
 67    17          13
           5     3    29
       19        2 11    53
    41     7
 71          23
    43          47
 73                79
 
> plotulamspir(100); \\ ULAMspiral1.png
  *** Ulam spiral: 101x101 matrix, p-flag=0
  *** matrix(101x101) 1252 DOTS

> plotulamspir(200); \\ ULAMspiral2.png
  *** Ulam spiral: 201x201 matrix, p-flag=0
  *** matrix(201x201) 4236 DOTS

Pascal[edit]

Rather than produce just splots, why not colour code them? Further, how about coding all the numbers according to the number of their first prime factor? The result looks a bit like a tartan rug. Alas, image files can't be presented, so a no show, but those with access to Turbo Pascal or similar can have a try. Amusingly enough, with black as colour zero reserved for N <= 1 (thus, the normal start square is black) and white as colour one for prime numbers, it becomes marginally convenient to regard two as the second prime... Without grid marking, finding the centre of the spiral is difficult, so showing N where it is a single digit helps. Encoding could be pressed forwards into different symbols, but enough already.

In the first part of the source are some support routines, from way back in the 1980s, written when the mainframe terminals only offered capitals and the habit lingered. They are there only so as to facilitate some gestures towards checking. The remainder is simple enough, and uses complex numbers to follow the spiral, which of course have to be implemented via ad-hoc code as they're not supported by the compiler. The scheme could be recast into the (line,column) form, counting downwards for the screen line, but array(i,j) = (x,y) means less standing upside down when devising the arithmetic for the directions, at the cost of a "downto" loop for output. An even more tricky scheme would be to ascertain N from (line,column) as the lines were written rather than compute the whole spiral first. Such a function exists.

 
Program Ulam; Uses crt;
{Concocted by R.N.McLean (whom God preserve), ex Victoria university, NZ.}
{$B- evaluate boolean expressions only so far as necessary.}
{$R+ range checking...}
 
FUNCTION Trim(S : string) : string;
var L1,L2 : integer;
BEGIN
L1 := 1;
WHILE (L1 <= LENGTH(S)) AND (S[L1] = ' ') DO INC(L1);
L2 := LENGTH(S);
WHILE (S[L2] = ' ') AND (L2 > L1) DO DEC(L2);
IF L2 >= L1 THEN Trim := COPY(S,L1,L2 - L1 + 1) ELSE Trim := '';
END; {Of Trim.}
 
FUNCTION Ifmt(Digits : integer) : string;
var S : string[255];
BEGIN
STR(Digits,S);
Ifmt := Trim(S);
END; { Ifmt }
Function min(i,j: integer): integer;
begin
if i <= j then min:=i else min:=j;
end;
Procedure Croak(Gasp: string); {A lethal word.}
Begin
WriteLn;
WriteLn(Gasp);
HALT; {This way to the egress...}
End;
var ScreenLine,ScreenColumn: byte; {Line and column position.}
{=========================enough support===================}
const Mstyle = 6; {Display different results.}
const StyleName: array[1..Mstyle] of string = ('IsPrime','First Prime Factor Index',
'First Prime Factor','Number of Prime Factors',
'Sum of Prime Factors','Sum of Proper Factors');
const OrderLimit = 49; Limit2 = OrderLimit*OrderLimit; {A 50-line screen has room for a heading.}
var Tile: array[1..OrderLimit,1..OrderLimit] of integer; {Alas, can't put [Order,Order], only constants.}
var FirstPrimeFactorIndex,FirstPrimeFactor,NumPFactor,SumPFactor,SumFactor: array[1..Limit2] of integer;
const enuffP = 17; {Given the value of Limit2.}
const Prime: array[1..enuffP] of integer = (1,2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53);
Procedure Prepare; {Various arrays are to be filled for the different styles.}
var i,j,p: integer;
Begin
for i:=1 to limit2 do {Alas, can't just put A:=0;}
begin {Nor clear A;}
FirstPrimeFactorIndex[i]:=1; {Prime[1] = 1, so this means no other divisor.}
FirstPrimeFactor[i]:=0;
NumPFactor[i]:=0;
SumPFactor[i]:=0;
SumFactor[i]:=1; {1 is counted as a proper factor.}
end;
FirstPrimeFactorIndex[1]:=0; {Fiddle, as 1 is not a prime number.}
SumFactor[1]:=0; {N is not a proper factor of N, so 1 has no proper factors...}
for i:=2 to enuffP do {Prime[1] = 1, Prime[2] = 2, so start with i = 2.}
begin
p:=Prime[i];
j:=p + p;
while j <= Limit2 do
begin
if FirstPrimeFactorIndex[j] = 1 then FirstPrimeFactorIndex[j]:=i;
if FirstPrimeFactor[j] = 0 then FirstPrimeFactor[j]:=p;
SumPFactor[j]:=SumPFactor[j] + p;
inc(NumPFactor[j]);
j:=j + p;
end;
end;
for i:=2 to Limit2 div 2 do {Step through all possible proper factors.}
begin {N is not a proper factor of N, so start at 2N,}
j:=2*i; {for which N is a proper factor of 2N.}
while j <= Limit2 do {Sigh. for j:=2*i:Limit2:i do ... Next i;}
begin
SumFactor[j]:=SumFactor[j] + i;
j:=j + i;
end;
end;
End; {Enough preparation.}
 
const enuffC = 11; {Perhaps the colours will highlight interesting patterns.}
const colour:array[0..enuffC] of byte = (black,white,LightRed,
LightMagenta,Yellow,LightGreen,LightCyan,LightBlue,LightGray,
Red,Green,DarkGray); {Colours on the screen don't always match their name!}
 
Procedure UlamSpiral(Order,Start,Style: integer); {Generate the numbers, then display.}
Function Encode(N: integer): integer; {Acording to Style, choose a result to show.}
Begin
if N <= 1 then Encode:=0
else
case style of
1:if FirstPrimeFactorIndex[N] = 1 then Encode:=1 else Encode:=0; {1 = Prime.}
2:Encode:=FirstPrimeFactorIndex[N];
3:Encode:=FirstPrimeFactor[N];
4:Encode:=NumPFactor[N];
5:Encode:=SumPFactor[N];
6:Encode:=SumFactor[N];
end;
End; {So much for encoding.}
var Place,Way: array[1..2] of integer; {Complex numbers.}
var m, {Middle.}
N, {Counter.}
length, {length of a side.}
lunge, {two lunges for each length.}
step {steps to make up a lunge of some length.}
: integer;
var i,j: integer; {Steppers.}
var code,it: integer; {Mess with the results.}
label XX; {Escape the second lunge.}
var OutF: text; {Utter drivel. It is a disc file.}
Begin
Write('Ulam Spiral, order ',Order,', start ',Start,', style ',style); {Start the heading.}
if style <= 0 then Croak('Must be a positive style');
if style > Mstyle then croak('Last known style is '+ifmt(Mstyle));
if Order > OrderLimit then Croak('Array OrderLimit is order '+IFmt(OrderLimit));
if Order mod 2 <>1 then Croak('The order must be an odd number!');
writeln(': ',StyleName[Style]); {Finish the heading. The pattern starts with line two.}
Assign(OutF,'Ulam.txt'); Rewrite(OutF); Writeln(OutF,'Ulam spiral: the codes for ',StyleName[style]);
m:=order div 2 + 1; {This is why Order must be odd.}
Place[1]:=m; Place[2]:=m; {Start at the middle.}
way[1]:=1; way[2]:=0; {Initial direction is along the x-axis.}
n:=Start;
for length:=1 to Order do {Advance through the lengths.}
for lunge:=1 to 2 do {Two lunges for each length.}
begin
for step:=1 to length do {Make the steps.}
begin
Tile[Place[1],Place[2]]:=N;
for i:=1 to 2 do Place[i]:=Place[i] + Way[i]; {Place:=Place + Way;}
N:=N + 1;
end;
if N >= Order*Order then goto XX; {Each corner piece is part of two lunges.}
i:=Way[1]; Way[1]:=-Way[2]; Way[2]:=i; {Way:=Way*(0,1) in complex numbers: (x,y)*(0,1) = (-y,x).}
end;
XX:for i:=order downto 1 do {Output: Lines count downwards, y runs upwards.}
begin {The first line is the topmost y.}
for j:=1 to order do {(line,column) = (y,x).}
begin {Work along the line.}
it:=Tile[j,i]; {Grab the number.}
code:=Encode(it); {Presentation scheme.}
Write(OutF,'(',it:4,':',code:2,')'); {Debugging...}
if FirstPrimeFactorIndex[it] > 1 then TextBackGround(Black) {Not a prime.}
else if it = 1 then TextBackGround(Black) {Darkness for one, also.}
else TextBackGround(White); {A prime number!}
TextColor(Colour[min(code,enuffC)]); {A lot of fuss for this!}
{Write(code:2);}
{Write(it:3);}
if it <= 9 then write(it) else Write('*'); {Thus mark the centre.}
end; {Next position along the line.}
if i > 1 then WriteLn; {Ending the last line would scroll the heading up.}
WriteLn(OutF); {But this is good for the text file.}
end; {On to the next line.}
Close(OutF); {Finished with the trace.}
{Some revelations to help in choosing a colour sequence.}
ScreenLine:=WhereY; ScreenColumn:=WhereX; {Gibberish to find the location.}
if Style > 1 then {Only the fancier styles go beyond 0 and 1.}
begin {So explain only for them.}
GoToXY(ScreenColumn + 1,ScreenLine - 4); {Unused space is to the right.}
TextColor(White); write('Colour sequence'); {Given 80-column displays.}
GoToXY(ScreenColumn + 1,ScreenLine - 3); {And no more than 50 lines.}
for i:=1 to enuffC do begin TextColor(Colour[i]); write(i); end; {My sequence.}
GoToXY(ScreenColumn + 1,ScreenLine - 2);
TextColor(White); write('From options');
GoToXY(ScreenColumn + 1,ScreenLine - 1);
for i:=1 to 15 do begin TextColor(i);write(i); end; {The options.}
end;
End; {of UlamSpiral.}
 
var start,wot,order: integer; {A selector.}
BEGIN {After all that.}
TextMode(Lo(LastMode) + Font8x8); {Gibberish sets 43 lines on EGA and 50 on VGA.}
ClrScr; TextColor(White); {This also gives character blocks that are almost square...}
WriteLn('Presents consecutive integers in a spiral, as per Stanislaw Ulam.');
WriteLn('Starting with 1, runs up to Order*Order.');
Write('What value for Order? (Limit ' + Ifmt(OrderLimit),'): ');
ReadLn(Order); {ReadKey needs no "enter", but requires decoding.}
if (order < 1) or (order > OrderLimit) then Croak('Out of range!'); {Oh dear.}
Prepare;
wot:=1; {The original task.}
Repeat {Until bored?}
ClrScr; {Scrub any previous stuff.}
UlamSpiral(Order,1,wot); {The deed!}
GoToXY(ScreenColumn + 1,ScreenLine); {Note that the last WriteLn was skipped.}
TextColor(White); Write('Enter 0, or 1 to '+Ifmt(Mstyle),': '); {Wot now?}
ReadLn(wot); {Receive.}
Until (wot <= 0) or (wot > Mstyle); {Alas, "Enter" must be pressed.}
END.
 

Perl[edit]

Translation of: python
use ntheory qw/is_prime/;
use Imager;
 
my $n = shift || 512;
my $start = shift || 1;
my $file = "ulam.png";
 
sub cell {
my($n, $x, $y, $start) = @_;
$y -= $n>>1;
$x -= ($n-1)>>1;
my $l = 2*(abs($x) > abs($y) ? abs($x) : abs($y));
my $d = ($y > $x) ? $l*3 + $x + $y : $l-$x-$y;
($l-1)**2 + $d + $start - 1;
}
 
my $black = Imager::Color->new('#000000');
my $white = Imager::Color->new('#FFFFFF');
my $img = Imager->new(xsize => $n, ysize => $n, channels => 1);
$img->box(filled=>1, color=>$white);
 
for my $y (0 .. $n-1) {
for my $x (0 .. $n-1) {
my $v = cell($n, $x, $y, $start);
$img->setpixel(x => $x, y => $y, color => $black) if is_prime($v);
}
}
 
$img->write(file => $file) or die "Cannot write $file: ", $img->errstr, "\n";
Output:

Creates an image file ulam.png in current directory similar to the one on MathWorld. The square dimension can be optionally specified.

Perl 6[edit]

sub MAIN($max = 160, $start = 1) {
(my %world){0}{0} = 0;
my $loc = 0+0i;
my $dir = 1;
my $n = $start;
my $side = 0;
 
while ++$side < $max {
step for ^$side;
turn-left;
step for ^$side;
turn-left;
}
 
braille-graphics %world;
 
sub step {
$loc += $dir;
%world{$loc.im}{$loc.re} = $n if (++$n).is-prime;
}
 
sub turn-left { $dir *= -i; }
sub turn-right { $dir *= i; }
 
}
 
sub braille-graphics (%a) {
my ($ylo, $yhi, $xlo, $xhi);
for %a.keys -> $y {
$ylo min= +$y; $yhi max= +$y;
for %a{$y}.keys -> $x {
$xlo min= +$x; $xhi max= +$x;
}
}
 
for $ylo, $ylo + 4 ...^ * > $yhi -> \y {
for $xlo, $xlo + 2 ...^ * > $xhi -> \x {
my $cell = 0x2800;
$cell += 1 if %a{y + 0}{x + 0};
$cell += 2 if %a{y + 1}{x + 0};
$cell += 4 if %a{y + 2}{x + 0};
$cell += 8 if %a{y + 0}{x + 1};
$cell += 16 if %a{y + 1}{x + 1};
$cell += 32 if %a{y + 2}{x + 1};
$cell += 64 if %a{y + 3}{x + 0};
$cell += 128 if %a{y + 3}{x + 1};
print chr($cell);
}
print "\n";
}
}
Output:
⠔⠀⠀⠀⢐⠀⠁⠀⠀⠀⢐⠁⠀⢀⠀⠄⠄⠀⢀⠀⠀⠅⢀⠁⢅⢄⠀⢀⠔⠁⠀⠀⠀⢀⢀⠀⠀⠀⠁⢀⢀⠀⠀⢔⠁⢔⠄⠀⢄⠐⠀⠀⢀⠁⠐⠄⠀⢑⠄⠁⠄⠀⠁⠄⠀⠀⠀⢐⠀⠄⠐⠀⢁⢀⠀⠀⠄⠀⢕⠐
⠄⠁⠁⠄⠀⠄⢀⠀⠐⠀⠀⠁⢁⢀⠐⠀⠀⠀⢁⠐⠄⠀⠀⠔⠀⢐⠁⠄⠀⠑⠀⢀⠁⠀⠐⠐⠁⠀⠄⠀⢀⠀⠀⠀⠐⠀⠐⠀⠅⠀⠀⢄⢀⠐⠁⠐⠄⠁⢀⠀⠀⠐⠁⠀⠀⠄⢄⠀⠕⠁⠀⠐⢄⠀⠀⢀⠐⠄⠁⠀
⠀⠀⢀⠁⢀⠀⠑⢀⠀⠄⠀⠀⠅⢑⠀⠁⠐⠀⠀⠐⠀⠄⠁⢄⠀⢑⠀⠄⢑⠀⠁⠀⢀⠑⢐⠀⠁⢀⠄⠐⢀⠄⠁⠀⠀⠀⠀⢀⠄⠀⠀⠑⠀⢀⠔⢁⠀⠀⠀⠀⠐⠁⠀⠑⢀⠀⠐⠀⢄⠔⢐⠄⠅⠐⠀⠅⢁⠀⠁⠁
⠅⢀⠄⠑⠀⠀⠅⠄⠀⢐⠐⠀⠀⠄⠀⢁⠄⠀⢔⢀⠁⠀⠔⠁⠑⢐⠀⠐⠀⠁⢑⠀⠀⢁⠀⠀⠄⠀⠀⠑⢀⠀⠄⠔⠁⠀⠄⠀⠐⢀⠀⠀⠔⠁⠀⠐⠀⠀⠐⠁⠐⠀⠀⢀⠄⠁⢁⠀⠀⠐⠀⠁⢐⠀⠐⠀⠄⠑⠐⠄
⠀⠀⠀⢐⠑⠑⢀⠁⠑⢀⠐⠀⠄⠀⠀⢀⢐⠕⠄⠀⠀⠀⠐⠀⠀⢀⠄⠀⠀⠀⠄⠐⠐⠀⠀⠁⢄⠐⠅⢀⠐⠄⠁⠐⠀⠅⢀⠐⢁⢀⠀⠁⠐⠕⠀⠀⠀⠀⢐⠀⠅⠐⠔⢁⠀⠐⠅⠐⠄⢀⠀⢄⠀⢀⠄⠀⠀⢀⠁⠐
⢀⠀⠀⢀⠁⠀⠀⠀⢁⠁⠐⠀⠁⢐⢀⠀⠁⠀⠔⠁⢄⠁⠁⠄⠀⢀⠄⠀⢐⠀⠔⠁⢀⠕⠁⢀⠁⠀⢀⠔⢐⠀⠀⠁⢀⠀⠀⢀⠔⠀⠄⠄⠁⠀⠄⢐⠄⠁⢁⠀⠄⠀⠀⠄⠀⢄⠀⢀⢀⠁⠄⢀⠄⠀⢀⠁⢁⠀⠀⠀
⠁⠄⠀⠀⠄⠀⠄⠀⠄⠑⢄⠔⠁⠀⠁⠀⠐⠀⠀⠀⠀⠀⢀⠀⠀⠄⠁⢁⠐⠀⠀⢀⠀⠄⠐⠀⢐⠀⠁⠀⠀⠁⠁⠄⠁⢄⠔⠀⠐⠀⠀⠔⢄⠀⠀⢐⠀⢅⠀⠁⢀⠀⠀⠀⠀⠀⠄⠀⠐⠀⠀⠀⠄⠀⠀⠀⠐⠀⠄⠄
⠀⠑⠐⠔⠀⢀⢀⠀⢁⠔⠁⢁⠄⠁⠀⠀⠀⠅⠀⢀⠀⠁⢀⠀⢄⠀⠀⠀⠐⠀⢀⠐⠁⢀⠀⠀⠀⢀⠁⠀⠐⠀⠄⢀⠔⢁⠀⠀⢅⠐⠑⠅⠀⠐⠀⢀⠁⢄⠀⠀⢁⠐⠄⠀⠐⢕⢀⠁⢀⠁⠑⠅⠀⢁⠐⠀⠁⠀⢁⢐
⢀⠁⠄⠀⠀⢄⠁⠄⠀⠀⠐⠅⠁⠁⢀⢀⢅⠄⠐⢁⠀⠄⠀⠄⠅⠑⢀⠔⢀⠀⠀⢁⠀⠕⠐⠀⠀⠐⢄⠐⢀⠄⠀⠁⢀⠁⢀⠀⠄⢀⠀⠀⠀⢀⠑⢐⠀⠀⠁⠄⠐⠁⠄⠄⠀⠀⠐⢄⢀⠀⠄⠄⠀⠀⠀⠄⢄⢀⠄⠀
⠐⠄⠐⠁⠀⠔⠑⠀⠀⠐⠀⠀⠑⠀⠐⠄⠀⠀⠐⠀⠁⢀⠄⠀⠀⢐⠀⠔⠀⠀⢄⠄⠁⢐⠀⠀⢄⠔⠀⢀⢐⠁⠅⢀⠀⠄⠐⠀⢐⠀⠁⢕⠄⠀⠀⢔⠁⠀⢐⠀⢀⠄⠑⠄⠀⠀⠄⠀⠀⠄⠐⠁⠄⠀⠐⠔⠄⠀⠀⠀
⢀⠐⢀⢐⠀⠀⠄⠑⠑⠐⠐⠀⠔⠑⠀⠐⠀⢀⠀⠀⢀⠄⠀⠁⢄⠀⠁⠀⢀⠁⢀⠀⠀⠀⠐⠄⠁⢐⠔⠅⢐⠅⠀⠀⠅⠀⠀⠀⠁⠀⠔⠄⠀⠔⢀⠀⠄⢁⠐⢁⢀⢁⢀⢀⢁⠄⠁⢀⠀⠀⢁⢑⠀⢀⢐⠁⠀⠀⠀⠁
⠀⠄⠅⠀⠁⠅⠁⢁⠄⠀⠀⢀⠀⢄⠀⠁⠁⢁⠀⠄⢅⢁⠄⠄⠐⢀⢀⠄⠁⠀⠀⠀⢄⠔⠁⢀⠐⠁⠄⠐⠀⠀⠁⢐⠀⠀⢀⢀⠀⠀⠀⠐⠀⠄⠐⠀⠀⠁⠄⠀⠁⠀⠀⠁⢄⠀⠁⢅⠀⠄⠁⠀⠁⠅⢀⠀⠀⠀⠐⠁
⠁⠀⠀⠀⠀⠀⠀⢄⠀⠐⢀⠀⠐⠄⠄⠁⠀⠔⠔⠄⠀⠁⠀⠐⠄⢀⠀⠄⠔⠀⠁⠀⠀⢐⢔⠁⠅⠀⠀⢐⠀⠀⠄⠄⠀⠑⠔⠀⠅⢀⠁⠔⢀⠀⢔⠀⠁⠐⠐⠐⢐⠔⠀⠐⠀⠐⠀⠀⠐⢐⠄⠐⠐⠀⠑⢐⠐⠑⠐⠐
⢀⠁⠁⠀⠀⢑⢀⠀⠑⢀⠀⢀⠀⠀⠁⢔⠀⠀⠀⠀⢀⢀⠁⠁⢄⠀⢁⠀⠀⠐⠁⢀⠐⢁⠐⠐⢁⠐⠀⢄⠐⠅⠀⢐⠄⢁⢀⠐⠄⠐⠐⠀⠀⠔⠀⠑⢔⢀⠑⠀⠀⠐⠑⠀⠀⠐⢀⢀⠑⠀⠐⢀⠀⠁⠐⠁⠀⢁⠀⠀
⠀⠔⠀⢀⠀⠀⢀⠑⠄⠁⠄⠄⢀⠐⠁⠁⠅⠁⢁⢀⠁⠀⢐⠀⠁⠅⢀⢁⠀⢀⠑⢑⠄⠀⠀⠄⠀⠁⢄⠀⢐⠄⠁⠑⢀⠅⢑⠀⠀⠀⠄⠄⢄⠄⠕⢀⠀⠔⢄⢀⠀⠀⠀⠁⢄⠄⠀⠁⠀⠐⠄⠀⠁⢀⠄⠔⠁⠀⠁⠄
⠀⠀⠐⠀⠄⠀⠀⢀⠄⠄⢄⠔⠐⢄⠀⠀⠄⠀⠀⠀⠀⠀⢄⠔⠐⠀⠔⠐⠀⠀⠔⠀⠀⢕⢔⠀⠁⢐⠁⢑⠐⠁⠀⠀⠀⢄⠀⠀⢅⠐⠑⠐⠀⠀⢐⠔⠀⠄⠀⠑⢔⠀⠀⠔⠀⠁⢀⠄⠀⠀⠀⠀⠀⠐⠀⠀⠐⠀⠐⠀
⠄⠐⠀⠄⠀⢀⠐⠀⢀⢐⠀⢀⠄⠀⢐⠀⠀⠀⠀⠐⠐⢄⠀⠀⠔⠀⢀⠀⠀⢐⢔⠀⢀⢄⠀⠄⢀⢀⠐⠁⢐⠅⠅⢀⠑⠄⠐⠐⠀⢀⠀⠁⠁⠑⠀⢁⠅⠀⠁⠄⠀⠁⠀⠀⠁⠁⠁⠐⠑⠁⠁⠀⢀⠐⢀⢀⠀⠁⠀⢀
⢁⢀⠄⠁⠐⠀⢁⠀⠀⠀⠀⠁⠀⢑⠀⢁⠐⠀⠀⠀⢁⠁⢐⠀⢀⠀⠀⠀⢕⢄⢁⢑⠄⠀⠔⢀⠐⠁⢀⠄⠐⠄⠄⢑⢄⠅⢄⠀⠁⢁⢀⠐⠁⢀⠀⠄⠀⠐⠀⠀⠀⢀⠀⠁⢄⠀⠄⠀⢀⠅⢁⠀⠀⢀⠀⠅⠄⠀⠑⠀
⠁⠄⠄⠁⠄⠀⠀⠀⠀⠁⠀⠄⠁⠀⠀⠄⠀⠀⠁⠄⠀⠁⠄⠀⠀⠄⠄⠄⠀⠀⠄⠀⠄⠁⠄⠀⠅⠄⠁⢕⢐⠀⢀⠔⠀⠔⠄⠑⠐⠀⠑⢔⠐⠁⠐⠐⠀⢄⠐⠐⠄⠀⠀⠀⠔⠑⠄⠄⠀⠀⠀⠀⢀⠄⠀⠀⠀⠁⢐⠔
⠐⠀⠑⢐⠁⠀⢐⠑⢁⢀⠐⢀⢐⠑⠁⠀⠀⢀⠀⠁⠑⠀⠑⢐⢀⠑⢐⠀⠁⢑⠀⠑⠐⠐⠐⠑⢐⠑⢑⠄⣔⢅⢁⢁⠐⢀⢁⢅⠁⠐⢐⠀⠀⠄⢀⢐⢅⢁⠀⠀⠀⠀⠐⠁⢁⠔⢀⢑⠁⢁⠐⢀⠀⠀⢄⢀⢁⢅⢀⠀
⢀⠀⠀⠁⠀⠀⠀⢐⢀⠁⠀⠀⠁⠀⠅⠀⠔⢁⢀⠀⠀⠀⢁⢁⠁⢐⠀⢀⠅⠅⢀⠀⠄⢁⠄⢄⠀⢕⠅⠑⢄⠀⠄⢄⢀⠄⢀⠄⠄⠀⢄⠀⠄⢄⠀⠀⢀⠄⢀⢀⠄⠀⠄⠄⠀⢀⠀⢄⠄⠀⢄⢀⠄⢀⢀⠄⠀⠄⠀⢀
⠐⢄⠀⠄⠀⠄⠐⠀⠀⠁⢀⠀⠅⠀⠄⠄⠀⠀⠀⢀⠔⠕⠄⠄⠑⠀⠀⠁⠀⠐⠔⢄⠀⠀⢄⠐⠔⢀⠁⢐⢀⠐⠄⠐⠁⠀⠄⠐⠐⠄⠁⠀⠐⠀⠄⠀⠑⠄⠐⠀⠀⠐⠀⠔⠀⠁⠔⠀⠁⠀⠀⠑⠄⠔⠀⠀⠀⠑⠐⠀
⠀⠀⢀⠄⠐⠀⠀⠀⢀⠄⠀⢑⢀⠁⠐⢀⠑⠀⠔⠐⢁⢐⠀⠐⢀⠀⠑⢐⠀⠀⢀⠐⢐⢔⠐⠄⢀⠁⠁⢐⠑⢄⢄⠑⠀⠁⠐⠐⢁⠐⠑⢁⠑⢀⢀⢀⠐⠁⢐⢐⠀⠐⠐⠀⢀⠑⢁⠁⠀⠀⠀⠑⠀⠁⢐⢀⠑⠀⢀⢀
⠁⢀⠀⠀⢁⠀⠀⠅⠀⠀⠅⠀⠀⠐⢀⢀⢀⠄⠀⠅⠀⢁⠔⠀⠁⢁⠁⠁⠑⢄⠀⠁⠁⢀⢀⠄⠑⢔⠀⠐⠔⠁⠀⠄⠀⠑⢀⠀⠕⠄⠀⠀⠄⢀⠀⠁⢄⠁⢄⠄⠐⠄⢄⠔⠀⠀⠐⠁⢀⠐⠀⠀⠅⠀⠀⠔⠀⢀⠁⠀
⠀⢄⠐⠁⠀⠐⠕⠀⠄⠐⠀⠐⠀⢀⠐⠐⠀⠀⠅⠀⠄⠁⢀⠄⠀⠄⠔⠑⢀⠀⠅⠀⠅⠄⠀⠄⠁⢀⠄⠀⢀⠀⢁⢀⠕⠀⠀⠑⠀⠐⠀⢄⠐⠁⢄⠄⠁⠐⠄⠐⢀⠀⠁⠄⠔⠀⢄⠀⠁⠄⠔⠁⢐⠄⠐⠀⠀⠑⢀⠔
⢀⠐⢀⠀⠀⠐⠄⠁⠐⠄⠐⠀⢀⠑⠁⠄⠀⠁⠐⠀⢀⠀⠁⢀⠀⠐⠐⠔⠁⢀⠀⠑⠀⠀⠐⠀⢔⠑⠀⢐⠀⢁⢀⠐⠀⢀⠐⢀⠄⠁⢄⠁⠀⠀⠁⠀⠀⠀⢐⢀⢁⢑⠀⢀⠑⠐⠁⠀⢀⢀⠀⠁⢀⢀⠀⠀⠐⢀⠀⠐
⢀⢁⠀⠀⢑⢅⢁⢄⢀⢀⠅⠀⠀⠄⢀⢁⢐⢁⢀⢅⢄⠀⠀⢀⢀⠐⠅⠁⠀⠀⢁⠐⠀⢀⠀⠀⠐⢀⠀⢀⠄⠅⠐⢐⠀⠀⠔⠁⠑⠐⠄⠀⠄⠀⠅⠁⠄⠐⠀⠀⠁⠁⠀⠄⠅⠀⠀⠄⠄⠅⠀⠄⠀⠄⠀⠁⠀⠀⠔⠀
⠁⠀⠀⠁⠀⠀⠀⢀⠄⠀⠀⠀⠀⠄⠄⠀⢀⠀⠐⢀⠀⠀⢄⠔⠄⠀⠄⠀⠀⠔⠕⢀⠔⠀⠀⠄⠄⠀⠁⠐⠀⠀⠕⢀⠕⠁⠀⠁⢑⠀⠀⢀⢀⠐⠄⠀⠑⠀⠀⠁⢄⠔⠑⢐⠀⠑⢄⠐⠀⠀⠐⠀⠀⠀⠀⠀⠄⠁⢀⠄
⠀⠁⠐⠀⠁⠀⠄⠀⠑⠀⠀⢀⠀⠐⠀⠄⠀⠑⠀⠀⢐⠀⠁⢅⠀⠀⠀⠐⠀⢀⠄⠀⢁⢄⠀⠁⠔⠑⠄⠀⠑⢄⠔⠁⢀⠀⠀⢄⠄⠀⠀⠐⠁⠁⢀⠐⠄⠀⠁⠐⠁⢀⢑⠁⠐⠐⢀⠑⠔⠀⠁⠀⢁⢀⠄⠁⢐⠀⠀⠀
⠀⠅⠁⢀⠐⠀⠁⠐⠀⠁⠐⢄⠀⢄⢀⠀⠄⢀⠁⢁⠄⠀⠐⠀⢑⠄⠀⠑⠐⠀⠁⠀⠁⠐⠐⠀⠁⠄⠄⢀⠄⠁⠐⢀⠄⠐⠀⠄⠀⠄⠀⠀⢀⠄⢀⢐⠀⠑⠀⠀⠄⢄⢄⠀⢅⠀⠀⠄⠀⠅⠀⠄⠐⢀⠀⠔⠅⠀⠄⢁
⠄⠀⠄⠄⠀⠄⠀⢀⠀⠐⠀⠀⠁⠀⠔⠄⠀⠀⠁⠀⠄⢄⠀⠐⠀⠀⠄⢑⠀⠁⠅⠀⠁⠀⢀⠄⠑⢀⠄⢀⢀⠔⢀⠀⠑⠄⠀⠅⠀⠀⠅⢕⠀⠐⢐⠀⠄⠕⠀⠀⢀⠀⠀⢀⠀⠁⠀⠀⠐⢀⠐⠁⢀⠔⠁⢐⠀⠀⠐⠀
⠀⠐⢁⢀⠐⠀⢀⠁⠀⠀⠁⠑⠄⠀⢁⠐⠁⠅⢀⠐⢀⠄⠀⠀⠐⠀⠅⢀⠐⢀⢀⠁⠅⢀⠀⠄⠔⠑⠁⠀⠁⠀⠐⠁⢀⠀⠀⢀⠀⠐⠄⠔⠐⠁⢄⠀⠅⢄⠑⠀⢀⠐⠀⠀⢁⢀⠀⢀⠁⢀⠁⠅⠁⠀⠁⠀⠀⠄⠀⠁
⠀⠀⢀⠀⠄⢁⠀⠀⠄⠀⢁⢁⠀⠀⠀⠐⠀⠄⠀⠐⠀⢀⢀⠁⠁⠄⠄⢀⠀⠀⠑⢀⠀⠑⠐⠁⠀⠀⠁⢐⠄⠀⢀⠐⠄⠐⢀⠁⠑⢀⠀⠀⠐⠀⢑⠄⠀⠁⠀⠅⠐⠄⠀⠀⠄⠀⠄⠁⠀⠄⢁⢀⠁⠁⠄⠀⠀⠀⠀⢄
⠑⠀⠀⠀⢀⠀⠁⠄⠐⠀⠀⠄⢄⠀⠐⠐⠀⠑⢁⠀⠔⠀⠀⠀⠀⠀⠕⢄⠀⠐⠀⢀⠔⠅⢀⠀⠐⠀⠅⢐⠀⠕⠐⢀⠀⠔⠀⠅⠀⠀⠀⠄⢀⠁⢀⠀⠀⠔⠀⠐⠁⢀⠀⠁⢀⠁⠀⠐⠐⠄⠐⠐⠄⠀⠀⠀⠀⠀⠔⠐
⠐⠀⢐⠀⠀⠀⢀⠀⠐⠐⠀⠀⠐⠀⠄⢀⠁⢄⠀⠑⢀⠀⠐⢀⢄⠀⠀⢀⠀⢅⢔⠁⠄⠐⠀⠁⠀⠑⠀⠀⠐⠁⠄⠀⢁⢀⠀⠁⠐⠁⠀⠀⠀⠀⠀⠀⠀⠀⠐⢀⠄⠀⢀⢔⠑⢅⠀⠐⢄⠁⢀⠄⢁⢀⠐⠀⠀⢀⢀⢑
⠀⠄⠅⢀⠁⠀⠀⠅⠁⠀⢄⠀⠁⠐⠁⢀⠀⠀⠀⠀⠀⠑⠀⠄⢀⠀⠀⢀⠐⠀⠀⢀⠁⠐⢀⠄⠁⢔⠄⠀⠄⠄⠑⠄⠁⠀⠀⠁⠐⠐⠄⠁⢄⠀⢀⠄⠁⠀⠔⠁⢀⠐⠄⠀⠀⠀⢁⢐⠀⠀⠄⠀⠀⢀⠀⠅⠀⠀⠀⠀
⠔⠀⠄⠀⢀⠄⠁⢀⠁⠄⠀⠀⠑⠀⠐⠁⠀⠐⠑⢀⠄⠄⠀⠀⢄⠀⠔⠔⢀⠀⠁⠀⠔⠀⢀⠄⠀⠀⠁⢐⠀⠑⠀⠀⠀⢅⠀⠀⢀⠀⠁⠄⠀⠁⢀⠀⠔⠐⠀⠀⢅⠀⠐⢀⠀⠀⠄⢀⠐⠔⠀⠁⠄⠀⠁⠀⠔⠐⠀⠀
⠀⠐⢀⠐⠀⠁⢀⠀⠀⠐⠐⢀⢄⠐⢄⠐⠀⠅⠀⠁⠁⠄⠐⢁⠄⠀⠀⢄⠀⠅⠔⠀⢁⠀⠐⠄⢀⠀⠁⠀⠐⠀⢀⠑⢀⠄⠀⠅⠀⠀⠅⠀⠀⢀⢔⠐⠄⠀⠁⠀⠐⠀⠀⢀⠑⠀⠄⠐⢁⢀⠀⢄⢄⠁⢀⠀⢐⠐⠁⠁
⠁⠄⠄⠀⠀⠁⠀⢐⠀⠐⠀⠄⢑⠀⠀⠑⠄⠁⢁⢀⠀⢑⠔⠁⠀⠄⠄⠀⢀⠀⠑⠔⠁⢁⠀⠄⢁⠔⠀⢀⠔⠀⢐⠀⠀⠀⠄⠄⠀⠐⠁⢁⠔⠁⠐⠐⠁⢀⢀⠀⠁⠔⠀⠀⠀⠅⠁⠀⠄⠀⠔⠁⢑⠀⠀⠀⠀⠀⠐⠀
⠁⠀⠅⠐⠀⠁⠀⠀⠐⠁⠀⠀⠕⠀⠀⠅⠀⠐⠀⠀⠕⠁⠀⠄⠅⠀⠀⠐⠀⠐⠅⠀⠀⠄⠀⠀⠀⠀⠀⠐⠀⠀⠀⠀⠁⠀⠀⠀⠄⠀⠐⠁⠀⠄⠁⠀⠁⠄⠀⠐⠄⠀⠅⠀⠀⠔⠁⠀⠀⠕⠀⠀⠀⠀⠀⠁⠀⠁⠀⠀

PicoLisp[edit]

(load "@lib/simul.l")
 
(de ceil (A)
(/ (+ A 1) 2) )
 
(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) ) ) ) ) )
 
(de ulam (N)
(let
(G (grid N N)
D '(north west south east .)
M (ceil N) )
(setq This
(intern
(pack
(char
(+ 96 (if (bit? 1 N) M (inc M))) )
M ) ) )
(=: V '_)
(with ((car D) This)
(for (X 2 (>= (* N N) X) (inc X))
(=: V (if (prime? X) '. '_))
(setq This
(or
(with ((cadr D) This)
(unless (: V) (pop 'D) This) )
((pop D) This) ) ) ) )
G ) )
 
(mapc
'((L)
(for This L
(prin (align 3 (: V))) )
(prinl) )
(ulam 9) )
 
(bye)
Output:
  _  _  _  _  .  _  .  _  _
  _  .  _  _  _  _  _  .  _
  .  _  .  _  _  _  .  _  _
  _  _  _  .  _  .  _  .  _
  _  _  .  _  _  .  .  _  .
  _  .  _  .  _  _  _  _  _
  .  _  _  _  .  _  _  _  _
  _  .  _  _  _  .  _  _  _
  .  _  _  _  _  _  .  _  _

PowerShell[edit]

 
function New-UlamSpiral ( [int]$N )
{
# Generate list of primes
$Primes = @( 2 )
For ( $X = 3; $X -le $N*$N; $X += 2 )
{
If ( -not ( $Primes | Where { $X % $_ -eq 0 } | Select -First 1 ) ) { $Primes += $X }
}
 
# Initialize variables
$X = 0
$Y = -1
$i = $N * $N + 1
$Sign = 1
 
# Intialize array
$A = New-Object 'boolean[,]' $N, $N
 
# Set top row
1..$N | ForEach { $Y += $Sign; $A[$X,$Y] = --$i -in $Primes }
 
# For each remaining half spiral...
ForEach ( $M in ($N-1)..1 )
{
# Set the vertical quarter spiral
1..$M | ForEach { $X += $Sign; $A[$X,$Y] = --$i -in $Primes }
 
# Curve the spiral
$Sign = -$Sign
 
# Set the horizontal quarter spiral
1..$M | ForEach { $Y += $Sign; $A[$X,$Y] = --$i -in $Primes }
}
 
# Convert the array of booleans to text output of dots and spaces
$Spiral = ForEach ( $X in 1..$N ) { ( 1..$N | ForEach { ( ' ', '.' )[$A[($X-1),($_-1)]] } ) -join '' }
return $Spiral
}
 
New-UlamSpiral 100
 
Output:
                           .     .                 .       .         . .     .               .     .
    .             .                                   .   .       .     .           .         .     
         .     .   .           .     .       .           .   .     .             .   .     .        
  .     .         . .           .   .                   .   .                 .       .     .       
       .             .   .           . .     .   .                             . .         .        
  . .       .   . .     .           .         .     .             .                     .     . .   
 . .     .             .   .     .             .   .       .   .     .       .   .                  
          .                       .                 . .               . .         .           .     
       .             .   .           .       .     .           .   .     .       .     .       .    
.             .         .     . .         . .         .     .           . .     .           .   .   
             .       .         .     .     .     . .     .         .     .       .     .   .        
                .     .     .             .     .   .     .       .                 .   .   .     . 
 .                                     .     . .   .                   .     .         .            
            .     .                     .     . .   .     .           . .   .     .                 
     .     .       .       .   .             .     .                           .     .   . . . . . .
. . .     . .             .           .     .         .                             .     .     .   
                   .                 .     .     .       .               .     .                    
        . .   . .       .         . .         .                             .         .           . 
     .     . .       . .           .     .               .     . .                                 .
.           .                 .         . .                 .     .   .           .                 
     . .         .         .         . .         .           . .         .     .     . . . . .   .  
    . . .         .     . .           .   .           . .     .   .     .     .             .       
                     .               . .         .                   .     .   .           .        
              . .     .       .     .     .         .       .                   .     .       .     
 .                           .     .   . .   .     .     .       .   . .     .   . .   .     . .    
.                 .                             .   .     .       .         .     .                 
 .         . .     .   .         .   .     .     .       .   . .                   . .              
. . . .   .       . .   .     . .           .         . .   . .               .                 .   
               .               . .                 .     .     .               .     .              
  .                 .             .     .     .     .       .         . . . . .     . .           . 
       . .     .       . .   .   .             .   .       .   .           .     .     . .         .
                                    .     .   . .   .             .   .                 .           
                 . .   . .     .     . .     .   . .                 . . .     . .       . .     .  
  .           . .     .       .     . .                     .     .             .   .     .     .   
               .                     . .     .   .           .     .           .           .        
                                                .   . .   .             . . .   . .   .     .     . 
         . .       .         . .               .   .       .   . .           .                      
            .     .           .     .   .           . .     .                     .     .           
             .         .     . .   . .     . .     .     .           .           .                  
.         . .             .   . .           .           .   .     . .     .                     .   
   .           .           .     .     .   .       .     .               .           .              
                          . .     .   .         .   . .   . . .                 .                 . 
 .         .   .   .       . . . .       .     .         . .   .     . .     .               .     .
      .     .                       .     .   . .               .     .     .                       
                                                 . .     .   .   . .   . . .   . .     . .         .
.       .     .     . . .     .   .   .   . .   .       .   . .         .           .     .       . 
                                                 . .   .                 .           .              
        . .   .     .     . .   .       .   . .     . . .     . . .               . .           . . 
           .   . .   . .     .   . . . . . . . .   .       .         . .         .             .    
                                                . . .           .           .     .                 
     .           . .   .     .             .   .  .. . . .   . . .     .       . . . .             .
    .         . . .       . .       .       . . .                                                   
   .                 .                       .   .                                                  
  .                       . .     .   . .   . .   .   . .   .   . .   .   . .       .     .   . .   
     . .       . .   .   .     .     .   .   .     .     . .   .       .     .     .   . .          
            .     .     .                     .           .           .           .                 
           . .     .         . .         . .     .   .   .       . .       .       .   .     .   .  
.         . . . .             . .     .   .           .       .     .         .     .           .   
         .                       .     .     .   . .                                                
  .       .           .                     . .   .     .   .     .   . . .         .               
   .   . .   .   .     . .       . . . .         . .     .     . .   . .   .       .   . .   . .    
      .                             .   .           . .                                             
 .         . .     .     .     .   . .     .     .   . .           .     .   . . .     . .         .
        .   .     . . . . .     . .       .         .       .     .             .   .               
               .           .               . .   . .         .     .                       .     .  
    .   .     .             .           .   .     .     .         . .     .       .   . .   . . .   
 . .         .       .       .       . .     .                 .             .     .   .       .    
      .     .           .     .   .       .           .   .     .           .     .           .     
 .                     . .                                 .     .   .     .         .   .         .
      .   .     .   . .       .   . .   .     .           .             .     . .     .         . . 
               .           .                 .     .   . .               .     .           .        
    .         .           .     .           .       .               .   .     .           . .     . 
       .             . . .       .     .   . .   .       .     .                       .     .     .
.                       .                 .                       .   .                             
           .     .           .             .     .   . .     .   .     .               . . . .   .  
.   .   .             . .     .                     .           . .           . .         . .     . 
   .                 .           .         .           . .     .   . .               .              
        . .           .                           . .         .       .   .   .   .             . . 
 . . . . . .     . .           .     .       .   .       .                                          
                              .               .       .   . .   . .               .     .     .     
       .         .           . .   .             .     .   .       .         .     .         . . .  
              . . .   .     . .   .     . .           .   .                   .           . .       
   .     .     .                 .                       .         .     . .               .     .  
    .         . .                 .     .   .     .     .                 . .         .   .   . .   
     .     .             .                 . .     .   .                 .       .       .     .   .
.               .             .     .     .   .     . .         . .               .                 
           .     .           .     . .               .     .     .             .             . .    
      . .         .     .     .   .       .         .                               .             . 
               .   .     . .         . .               .     .                   .   .              
  .       .         .                       . .   .       .     .   .       .             . . .   . 
     .   .         .                             .       .                 .   . .           . .   .
      .                 .   . .   .       .               .     .     . .           .               
                 .       .                 .         .     .             .   . .     .              
.         . .         .       .         .     .     .       .   .     . .         . .               
             .           .             .     .   . .   .                 .     .           .     .  
  . .                 .         . .         . .   .     .                   .     .   .           . 
 .       .         .       .               . .         .             .   . .           .     .      
    .       .         .           .     . .                           . .     .   . .               
       .   .             .   . .     .                     .     .             .     .     .       .
                . .           .     .   .     .                 . .           .     .   .           

Python[edit]

# coding=UTF-8
from __future__ import print_function, division
from math import sqrt
 
def cell(n, x, y, start=1):
d, y, x = 0, y - n//2, x - (n - 1)//2
l = 2*max(abs(x), abs(y))
d = (l*3 + x + y) if y >= x else (l - x - y)
return (l - 1)**2 + d + start - 1
 
def show_spiral(n, symbol='# ', start=1, space=None):
top = start + n*n + 1
is_prime = [False,False,True] + [True,False]*(top//2)
for x in range(3, 1 + int(sqrt(top))):
if not is_prime[x]: continue
for i in range(x*x, top, x*2):
is_prime[i] = False
 
cell_str = lambda x: f(x) if is_prime[x] else space
f = lambda _: symbol # how to show prime cells
 
if space == None: space = ' '*len(symbol)
 
if not len(symbol): # print numbers instead
max_str = len(str(n*n + start - 1))
if space == None: space = '.'*max_str + ' '
f = lambda x: ('%' + str(max_str) + 'd ')%x
 
for y in range(n):
print(''.join(cell_str(v) for v in [cell(n, x, y, start) for x in range(n)]))
print()
 
show_spiral(10, symbol=u'♞', space=u'♘') # black are the primes
show_spiral(9, symbol='', space=' - ')
# for filling giant terminals
#show_spiral(1001, symbol='*', start=42)
Output:
♘♘♘♞♘♘♘♘♘♘
♘♘♘♘♞♘♞♘♘♘
♘♞♘♘♘♘♘♞♘♞
♞♘♞♘♘♘♞♘♘♘
♘♘♘♞♘♞♘♞♘♘
♘♘♞♘♘♞♞♘♞♘
♘♞♘♞♘♘♘♘♘♘
♞♘♘♘♞♘♘♘♘♘
♘♞♘♘♘♞♘♘♘♞
♞♘♘♘♘♘♞♘♘♘

 -  -  -  - 61  - 59  -  - 
 - 37  -  -  -  -  - 31  - 
67  - 17  -  -  - 13  -  - 
 -  -  -  5  -  3  - 29  - 
 -  - 19  -  -  2 11  - 53 
 - 41  -  7  -  -  -  -  - 
71  -  -  - 23  -  -  -  - 
 - 43  -  -  - 47  -  -  - 
73  -  -  -  -  - 79  -  - 

R[edit]

My own plotting helper function plotmat() was used and made it possible. You can find it here on RC (Brownian tree in R) .

Note
  • All pictures are ready to be uploaded, when it would be allowed again.
Translation of: PARI/GP
Works with: R version 3.3.1 and above
File:UlamSpiralR1.png
Output UlamSpiralR1.png
File:UlamSpiralR2.png
Output UlamSpiralR2.png
 
## Plotting Ulam spiral (for primes) 2/12/17 aev
## plotulamspirR(n, clr, fn, ttl, psz=600), where: n - initial size;
## clr - color; fn - file name; ttl - plot title; psz - picture size.
##
require(numbers);
plotulamspirR <- function(n, clr, fn, ttl, psz=600) {
cat(" *** START:", date(), "n=",n, "clr=",clr, "psz=", psz, "\n");
if (n%%2==0) {n=n+1}; n2=n*n;
x=y=floor(n/2); xmx=ymx=cnt=1; dir="R";
ttl= paste(c(ttl, n,"x",n," matrix."), sep="", collapse="");
cat(" ***", ttl, "\n");
M <- matrix(c(0), ncol=n, nrow=n, byrow=TRUE);
for (i in 1:n2) {
if(isPrime(i)) {M[x,y]=1};
if(dir=="R") {if(xmx>0) {x=x+1;xmx=xmx-1}
else {dir="U";ymx=cnt;y=y-1;ymx=ymx-1}; next};
if(dir=="U") {if(ymx>0) {y=y-1;ymx=ymx-1}
else {dir="L";cnt=cnt+1;xmx=cnt;x=x-1;xmx=xmx-1}; next};
if(dir=="L") {if(xmx>0) {x=x-1;xmx=xmx-1}
else {dir="D";ymx=cnt;y=y+1;ymx=ymx-1}; next};
if(dir=="D") {if(ymx>0) {y=y+1;ymx=ymx-1}
else {dir="R";cnt=cnt+1;xmx=cnt;x=x+1;xmx=xmx-1}; next};
};
plotmat(M, fn, clr, ttl,,psz);
cat(" *** END:",date(),"\n");
}
 
## Executing:
plotulamspirR(100, "red", "UlamSpiralR1", "Ulam Spiral: ");
plotulamspirR(200, "red", "UlamSpiralR2", "Ulam Spiral: ",1240);
 
Output:
> plotulamspirR(100, "red", "UlamSpiralR1", "Ulam Spiral: ");
 *** START: Sun Feb 12 12:03:34 2017 n= 100 clr= red psz= 600 
 *** Ulam Spiral: 101x101 matrix. 
 *** Matrix( 101 x 101 ) 1232 DOTS
 *** END: Sun Feb 12 12:03:37 2017 

> plotulamspirR(200, "red", "UlamSpiralR2", "Ulam Spiral: ",1240);
 *** START: Sun Feb 12 12:03:51 2017 n= 200 clr= red psz= 1240
 *** Ulam Spiral: 201x201 matrix. 
 *** Matrix( 201 x 201 ) 4196 DOTS
 *** END: Sun Feb 12 12:04:07 2017 

Racket[edit]

Translation of: Python
#lang racket
(require (only-in math/number-theory prime?))
 
(define ((cell-fn n (start 1)) x y)
(let* ((y (- y (quotient n 2)))
(x (- x (quotient (sub1 n) 2)))
(l (* 2 (if (> (abs x) (abs y)) (abs x) (abs y))))
(d (if (> y x) (+ (* l 3) x y) (- l x y))))
(+ (sqr (- l 1)) d start -1)))
 
(define (show-spiral n
#:symbol (smb "# ")
#:start (start 1)
#:space (space (and smb (make-string (string-length smb) #\space))))
(define top (+ start (sqr n) 1))
(define cell (cell-fn n start))
(define print-cell
(if smb
(λ (i p?) (display (if p? smb space)))
(let* ((max-len (string-length (~a (+ (sqr n) start -1))))
(space (or space (make-string (string-length (~a (+ (sqr n) start -1))) #\_))))
(λ (i p?)
(display (if p? (~a #:width max-len i #:align 'right) space))
(display #\space)))))
 
(for* ((y (in-range 1 (add1 n))) #:when (unless (= y 1) (newline)) (x (in-range 1 (add1 n))))
(define c (cell x y))
(define p? (prime? c))
(print-cell c p?))
(newline))
 
(show-spiral 9 #:symbol #f)
(show-spiral 10 #:symbol "♞" #:space "♘") ; black are the primes
(show-spiral 50 #:symbol "*" #:start 42)
; for filling giant terminals
; (show_spiral 1001 "*" 42)
Output:
37 __ __ __ __ __ 31 __ 89 
__ 17 __ __ __ 13 __ __ __ 
__ __  5 __  3 __ 29 __ __ 
__ 19 __ __  2 11 __ 53 __ 
41 __  7 __ __ __ __ __ __ 
__ __ __ 23 __ __ __ __ __ 
43 __ __ __ 47 __ __ __ 83 
__ __ __ __ __ 79 __ __ __ 
11 __ __ __ __ __ __ __ __ 
♘♘♘♞♘♞♘♘♘♞
♞♘♘♘♘♘♞♘♞♘
♘♞♘♘♘♞♘♘♘♘
♘♘♞♘♞♘♞♘♘♘
♘♞♘♘♞♞♘♞♘♞
♞♘♞♘♘♘♘♘♘♘
♘♘♘♞♘♘♘♘♘♘
♞♘♘♘♞♘♘♘♞♘
♘♘♘♘♘♞♘♘♘♘
♞♘♘♘♘♘♘♘♘♘
    * *     *                     * *             
     *         * *   *     * *               * *  
      *                     * *               *   
 *     *           * *   *     *             *   *
*       *         *     * *     *   * *           
       * *         *           *     * *   * * * *
    *           *     * *           *   * *       
           *     *     *         *       *        
  * *     * *         * *         *     *   *     
         *   *       *         *       *   *     *
      *     * *         * *           *           
 *     * *         *       *         * * *     *  
    *     * *   *     *     * *     *             
         * *   * *           *     *              
        *       *     * *         *   *   * * * * 
             *       *     *   * *               *
              *     *         * *                 
 *                   *   * *   * *       *     *  
    *           *     * *     *   *     *       * 
   *                 * *     *     *     *        
  *     * *     *     * *   *       *   * * *     
 *           *     *     * *   *     * *         *
*     *       *     *     *                       
 *       *       * * *   *             *   * *    
                      * *   *             *   * * 
   *       *   * *   *       *           *     *  
      *   *       * *     *     * * *     * * *   
 *                 *     *     * *         *      
  *         * *   *                               
   * * *     * * *     *     * *   *   * *   * * *
    *           * *           *   * *     *   *   
   *           *     *     *             *     *  
      *   *   *   *             *             * * 
       *     *     *       *   *       *         *
        *   * *   *           *       *     *     
 *   * *   *         *     *     * * *     * *   *
          * *   *     *     * *                   
         *       *     *   *       *              
      * *   * *   *             *   * *           
       *     *     *       *     *         *      
      *     *     *       *     *     *           
 *   *     *           *         *                
    *       *                 *         *         
           *           *     *   *     *          
  *           *   * *         *           * * * * 
               *     *   * *   * *         *     *
*     * *         *             *         *       
   *     *       *               * *   *       *  
    *           *     *     *             *   *   
               *       *   *           *          

REXX[edit]

Programming note for the showing of the spiral:   because images can't be uploaded at this time on Rosetta Code, the glyphs for primes was chosen to be a solid glyph   (or in ASCII or XML terminology, a "block").

This then allows the REXX program to compress two rows of the Ulam spiral into one by processing two rows at a time by comparing each character to the character on the next line   (when comparing two lines as a pair):

  • if a char on row   k   is a block, and the char on row   k+1   is a block, then a   "block"   is used.
  • if a char on row   k   is a block, and the char on row   k+1   is a blank, then a   "UHblk"   is used.
  • if a char on row   k   is a blank, and the char on row   k+1   is a block, then a   "LHblk"   is used.
  • if a char on row   k   is a blank, and the char on row   k+1   is a blank, then a     blank   is used.

For codepage 437:

  •   a "block" is 'db'x     █       (a full block)
  •   a "LHblk" is 'dc'x     ▄       (a Lower Half block)
  •   a "UHblk" is 'df'x     ▀       (a Upper Half block)

Or, to show all three characters in the (above) ordered next to each other (separated by a blank):   █ ▄ ▀

This allows the displaying of the Ulam prime spiral to keep a (mostly) square aspect ratio.

The characters chosen allow for the HTML on Rosetta Code to shrink (via STYLE font-size) the displayed output to half their normal height.

counter-clockwise[edit]

/*REXX program shows counter─clockwise  Ulam spiral  of primes shown in a square matrix.*/
parse arg size init char . /*obtain optional arguments from the CL*/
if size=='' | size=="," then size=79 /*Not specified? Then use the default.*/
if init=='' | init=="," then init= 1 /* " " " " " " */
if char=='' then char="█" /* " " " " " " */
tot=size**2 /*the total number of numbers in spiral*/
/*define the upper/bottom right corners*/
uR.=0; bR.=0; do od=1 by 2 to tot; _=od**2+1; uR._=1; _=_+od; bR._=1; end /*od*/
/*define the bottom/upper left corners.*/
bL.=0; uL.=0; do ev=2 by 2 to tot; _=ev**2+1; bL._=1; _=_+ev; uL._=1; end /*ev*/
 
app=1; bigP=0; #p=0; inc=0; minR=1; maxR=1; r=1; $=0; $.=;  !.=
/*▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ construct the spiral #s.*/
do i=init for tot; r=r+inc; minR=min(minR,r); maxR=max(maxR,r)
x=isPrime(i); if x then bigP=max(bigP,i); #p=#p+x /*bigP, #primes.*/
if app then $.r=$.r || x /*append token.*/
else $.r= x || $.r /*prepend token.*/
if uR.i then do; app=1; inc=+1; iterate /*i*/; end /*advance ↓ */
if bL.i then do; app=0; inc=-1; iterate /*i*/; end /* " ↑ */
if bR.i then do; app=0; inc= 0; iterate /*i*/; end /* " ► */
if uL.i then do; app=1; inc= 0; iterate /*i*/; end /* " ◄ */
end /*i*/ /* [↓] pack two */
/*lines ──► one.*/
do j=minR to maxR by 2; jp=j+1; $=$+1 /*fold two lines*/
do k=1 for length($.j); top=substr($.j,k,1) /*the 1st line.*/
bot=word(substr($.jp,k,1) 0,1) /*the 2nd line.*/
if top then if bot then !.$= !.$'█' /*has top & bot.*/
else !.$= !.$'▀' /*has top,¬ bot.*/
else if bot then !.$= !.$'▄' /*¬ top, has bot*/
else !.$= !.$' ' /*¬ top, ¬ bot*/
end /*k*/
end /*j*/ /* [↓] show the prime spiral matrix.*/
do m=1 for $; say !.m; end /*m*/
say; say init 'is the starting point,' ,
tot 'numbers used,' #p "primes found, largest prime:" bigP
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
isPrime: procedure; parse arg x; if wordpos(x,'2 3 5 7 11 13 17 19') \==0 then return 1
if x<17 then return 0; if x// 2 ==0 then return 0
if x// 3 ==0 then return 0
/*get the last digit*/ parse var x '' -1 _; if _==5 then return 0
if x// 7 ==0 then return 0
if x//11 ==0 then return 0
if x//13 ==0 then return 0
 
do j=17 by 6 until j*j > x; if x//j ==0 then return 0
if x//(j+2) ==0 then return 0
end /*j*/
return 1

output   when the default inputs are used:
(Shown at three-quarter size.)

      ▀     ▀     ▀          ▄  ▀  ▄ ▄▀  ▄▀     ▀       ▀    ▄     ▄      ▀  ▄▀
 ▄▀     ▀▄       ▄   ▄        ▀    ▄▀ ▀  ▄▀     ▀           ▀ ▀   ▀  ▄  ▀  ▄
▀ ▀      ▄      ▀          ▄▀    ▄▀    ▄    ▀  ▄               ▄     ▄    ▀
▀▄ ▄▀ ▀    ▄ ▄▀         ▀▄▀    ▄    ▀          ▄     ▄ ▄          ▀         ▀
  ▀    ▄         ▄  ▀      ▄ ▄▀ ▀      ▄          ▀▄ ▄  ▀   ▀  ▄     ▄  ▀  ▄ ▄
        ▀  ▄  ▀ ▀          ▄▀▄  ▀      ▄    ▀ ▀     ▀   ▀  ▄  ▀  ▄  ▀▄
    ▀ ▀     ▀      ▄▀    ▄▀  ▄ ▄▀  ▄     ▄▀    ▄  ▀    ▄   ▄ ▄     ▄  ▀▄ ▄  ▀▄
 ▄ ▄    ▀▄   ▄         ▄   ▄     ▄    ▀▄  ▀    ▄▀  ▄ ▄  ▀         ▀     ▀▄ ▄
▀    ▄  ▀ ▀   ▀     ▀▄▀▄          ▀      ▄  ▀ ▀▄  ▀ ▀▄              ▀▄     ▄
     ▄    ▀  ▄ ▄   ▄   ▄▀     ▀     ▀▄   ▄▀      ▄▀  ▄      ▀ ▀ ▀▄▀ ▀  ▄  ▀ ▀▄
       ▄ ▄   ▄ ▄     ▄    ▀▄ ▄  ▀  ▄▀ ▀▄ ▄▀             ▀  ▄▀▄ ▄     ▄ ▄      ▀
    ▀▄▀     ▀       ▀     ▀▄▀▄     ▄   ▄          ▀▄    ▀▄           ▄▀   ▀
 ▄       ▄         ▄ ▄               ▄▀  ▄▀ ▀   ▀▄   ▄ ▄      ▀ ▀ ▀▄  ▀ ▀   ▀
  ▀▄    ▀    ▄     ▄▀▄   ▄▀▄  ▀  ▄ ▄     ▄▀ ▀  ▄  ▀        ▄           ▄▀     ▀
▀ ▀  ▄          ▀▄  ▀ ▀▄     ▄   ▄▀      ▄    ▀▄  ▀     ▀ ▀    ▄▀          ▄
 ▄   ▄   ▄      ▀▄▀▄ ▄ ▄▀   ▀  ▄     ▄▀   ▀ ▀  ▄▀▄▀ ▀▄     ▄ ▄     ▄  ▀
  ▀                       ▀     ▀   ▀ ▀▄ ▄     ▄   ▄  ▀▄ ▄  ▀▄ ▄ ▄▀  ▄ ▄     ▄
    ▀     ▀ ▀ ▀     ▀   ▀   ▀   ▀ ▀   ▀▄ ▄   ▄▀   ▀ ▀         ▀▄          ▀▄
▀▄  ▀▄ ▄  ▀▄ ▄  ▀ ▀▄  ▀▄ ▄ ▄ ▄▀▄ ▄▀▄▀▄   ▄▀ ▀ ▀  ▄  ▀ ▀ ▀  ▄ ▄         ▄▀ ▀
       ▄ ▄   ▄     ▄             ▄   ▄▀ █▄▀▄ ▄ ▄   ▄ ▄▀▄     ▄    ▀  ▄ ▄▀▄ ▄
    ▀ ▀ ▀  ▄    ▀ ▀       ▀       ▀▄▀ ▀▄
     ▄ ▄   ▄   ▄▀ ▀  ▄  ▀  ▄▀ ▀▄  ▀▄▀   ▀▄  ▀ ▀▄ ▄▀  ▄▀ ▀   ▀▄  ▀ ▀▄     ▄▀  ▄
 ▄▀▄    ▀▄    ▀    ▄ ▄         ▄ ▄  ▀  ▄   ▄   ▄▀      ▄ ▄  ▀    ▄      ▀▄   ▄
▀ ▀ ▀ ▀             ▀ ▀▄    ▀▄  ▀  ▄   ▄ ▄  ▀       ▀     ▀         ▀     ▀
▀  ▄   ▄    ▀▄ ▄       ▄ ▄ ▄ ▄    ▀ ▀  ▄▀▄    ▀▄  ▀  ▄ ▄▀  ▄▀▄▀ ▀▄       ▄▀  ▄
 ▄ ▄     ▄     ▄     ▄   ▄▀▄  ▀  ▄     ▄  ▀▄▀▄           ▄     ▄   ▄ ▄ ▄     ▄
  ▀  ▄  ▀ ▀ ▀ ▀ ▀▄    ▀ ▀       ▀▄ ▄   ▄ ▄▀       ▀▄    ▀▄            ▀   ▀
   ▄▀      ▄      ▀▄       ▄ ▄▀   ▀▄    ▀     ▀      ▄  ▀ ▀     ▀  ▄    ▀▄  ▀▄▀
  ▀          ▄▀▄    ▀   ▀       ▀           ▀   ▀▄    ▀▄   ▄     ▄▀     ▀  ▄
▀    ▄▀   ▀ ▀    ▄  ▀   ▀ ▀   ▀    ▄▀    ▄   ▄ ▄▀             ▀▄    ▀▄▀     ▀
    ▀      ▄ ▄ ▄▀     ▀▄     ▄   ▄▀▄   ▄  ▀    ▄     ▄    ▀   ▀     ▀        ▄
 ▄     ▄      ▀    ▄            ▀▄     ▄   ▄ ▄     ▄   ▄▀   ▀▄               ▄
           ▄▀ ▀     ▀  ▄         ▄        ▀  ▄ ▄     ▄▀ ▀▄ ▄        ▀ ▀    ▄
▀▄     ▄ ▄  ▀        ▄     ▄       ▄   ▄▀ ▀    ▄    ▀       ▀   ▀   ▀   ▀
       ▄           ▄▀▄   ▄          ▀  ▄    ▀▄  ▀▄▀   ▀ ▀▄         ▄    ▀▄    ▀
    ▀▄▀ ▀   ▀     ▀ ▀  ▄▀     ▀ ▀           ▀  ▄▀        ▄     ▄ ▄  ▀
 ▄  ▀ ▀        ▄        ▀     ▀  ▄▀▄    ▀▄   ▄▀                ▄▀ ▀    ▄    ▀
 ▄    ▀▄           ▄▀    ▄▀▄    ▀   ▀     ▀▄▀    ▄    ▀▄▀            ▄  ▀
     ▄  ▀▄    ▀▄ ▄  ▀   ▀  ▄ ▄  ▀         ▀  ▄     ▄                   ▄  ▀▄
▀         ▀                       ▀ ▀   ▀       ▀     ▀   ▀       ▀

1 is the starting point, 6241 numbers used, 811 primes found, largest prime: 6229

output   when the following input is used:   ,   41
(Shown at three-quarter size.)

    ▀▄     ▄▀    ▄      ▀  ▄      ▀▄▀  ▄      ▀     ▀     ▀          ▄  ▀  ▄ ▄▀
            ▀   ▀ ▀▄           ▄    ▀  ▄▀ ▀     ▀▄       ▄   ▄        ▀    ▄▀
 ▄▀▄   ▄▀   ▀▄▀    ▄ ▄    ▀▄   ▄ ▄  ▀     ▀      ▄      ▀          ▄▀    ▄▀ ▀▄▀
▀ ▀ ▀ ▀    ▄▀  ▄ ▄            ▀  ▄      ▀    ▄▀    ▄ ▄▀         ▀▄▀    ▄
▀  ▄   ▄    ▀▄  ▀  ▄       ▄  ▀  ▄   ▄  ▀ ▀▄  ▀          ▄  ▀      ▄ ▄▀    ▄▀
 ▄ ▄     ▄         ▄ ▄  ▀▄▀               ▀ ▀      ▄  ▀ ▀          ▄▀ ▀ ▀▄    ▀
  ▀  ▄  ▀ ▀ ▀   ▀▄         ▄ ▄▀        ▄  ▀  ▄ ▄   ▄▀      ▄▀    ▄▀▄
   ▄▀      ▄    ▀  ▄ ▄  ▀  ▄      ▀              ▄ ▄▀          ▄    ▀     ▀ ▀
  ▀          ▄▀▄    ▀▄        ▀ ▀   ▀     ▀▄▀▄              ▀▄▀  ▄
▀    ▄▀   ▀ ▀    ▄    ▀▄         ▄▀ ▀  ▄▀▄    ▀▄   ▄ ▄     ▄ ▄ ▄ ▄▀  ▄   ▄    ▀
    ▀      ▄ ▄ ▄▀     ▀ ▀      ▄  ▀  ▄ ▄      ▀    ▄▀ ▀▄ ▄▀
 ▄     ▄      ▀     ▀    ▄▀▄    ▀    ▄▀▄        ▀▄     ▄▀  ▄▀    ▄ ▄   ▄
           ▄▀ ▀   ▀ ▀   ▀  ▄▀▄      ▀  ▄ ▄    ▀      ▄▀▄ ▄     ▄             ▄
▀▄     ▄ ▄  ▀  ▄ ▄    ▀▄ ▄ ▄   ▄  ▀  ▄    ▀▄ ▄     ▄▀               ▀       ▀
       ▄            ▀    ▄▀▄  ▀▄▀    ▄ ▄    ▀    ▄▀   ▀   ▀ ▀ ▀ ▀▄▀ ▀ ▀▄    ▀
    ▀▄▀ ▀     ▀         ▀    ▄     ▄▀     ▀  ▄▀▄▀▄       ▄     ▄     ▄ ▄     ▄
 ▄  ▀ ▀          ▄            ▀     ▀▄ ▄▀ ▀  ▄▀   ▀▄    ▀▄      ▀    ▄      ▀
 ▄      ▀    ▄     ▄▀           ▀   ▀▄▀▄   ▄▀  ▄    ▀▄ ▄▀ ▀ ▀    ▄  ▀ ▀  ▄
    ▀      ▄     ▄▀     ▀ ▀  ▄  ▀  ▄    ▀▄▀            ▄   ▄ ▄    ▀        ▄  ▀
▀  ▄     ▄▀     ▀▄    ▀  ▄    ▀  ▄ ▄▀▄ ▄▀   ▀▄           ▄▀   ▀▄▀   ▀ ▀     ▀
 ▄      ▀▄     ▄   ▄       ▄   ▄ ▄   ▄▀   ▀    ▄▀▄▀ ▀     ▀▄▀ ▀         ▀▄   ▄▀
  ▀  ▄  ▀  ▄     ▄    ▀   ▀       ▀▄▀     ▀  ▄ ▄   ▄   ▄ ▄   ▄ ▄ ▄ ▄ ▄     ▄
 ▄       ▄   ▄    ▀▄ ▄ ▄    ▀▄▀▄ ▄▀▄    ▀     ▀   ▀ ▀    ▄▀   ▀▄    ▀     ▀
       ▄▀      ▄   ▄▀          ▄▀  ▄  ▀     ▀   ▀      ▄      ▀ ▀▄          ▀
▀ ▀                   ▀▄  ▀  ▄▀▄   ▄▀       ▀  ▄▀  ▄ ▄▀    ▄▀▄   ▄ ▄ ▄  ▀  ▄ ▄
 ▄ ▄▀ ▀    ▄   ▄ ▄   ▄ ▄▀  ▄▀▄   ▄    ▀▄    ▀▄ ▄  ▀                 ▀▄
 ▄      ▀     ▀▄         ▄▀  ▄ ▄  ▀▄    ▀   ▀    ▄  ▀▄▀    ▄       ▄  ▀▄ ▄  ▀▄
  ▀     ▀ ▀▄▀         ▀▄▀    ▄▀    ▄▀      ▄▀    ▄▀    ▄          ▀     ▀▄ ▄
   ▄▀ ▀     ▀▄   ▄   ▄▀     ▀▄          ▀      ▄  ▀      ▄          ▀▄     ▄
  ▀▄     ▄   ▄ ▄    ▀       ▀  ▄   ▄ ▄  ▀     ▀▄  ▀     ▀  ▄▀ ▀ ▀▄▀ ▀  ▄  ▀ ▀▄
     ▄▀           ▀    ▄ ▄      ▀  ▄  ▀   ▀ ▀   ▀▄▀        ▄▀  ▄     ▄ ▄      ▀
 ▄  ▀▄    ▀▄   ▄▀   ▀▄    ▀      ▄▀    ▄     ▄    ▀ ▀   ▀  ▄   ▄     ▄▀   ▀
 ▄       ▄   ▄▀ ▀▄ ▄            ▀  ▄    ▀   ▀    ▄   ▄  ▀  ▄      ▀▄  ▀ ▀   ▀
  ▀ ▀ ▀ ▀ ▀ ▀       ▀   ▀    ▄ ▄   ▄ ▄▀   ▀      ▄▀           ▀        ▄▀     ▀
     ▄   ▄▀   ▀ ▀▄         ▄       ▄  ▀  ▄    ▀▄          ▀     ▀    ▄     ▄
       ▄▀        ▄     ▄ ▄  ▀      ▄ ▄         ▄ ▄▀        ▄  ▀ ▀▄ ▄▀
▀   ▀▄▀                ▄▀ ▀    ▄    ▀             ▀    ▄▀  ▄▀▄▀  ▄▀    ▄ ▄   ▄
▀  ▄▀    ▄    ▀▄▀            ▄  ▀      ▄    ▀       ▀▄   ▄            ▀   ▀
  ▀  ▄     ▄                   ▄  ▀▄           ▄  ▀ ▀     ▀  ▄▀ ▀   ▀ ▀
▀       ▀     ▀   ▀       ▀                 ▀         ▀     ▀     ▀ ▀     ▀

41 is the starting point, 6241 numbers used, 805 primes found, largest prime: 6277

output   with an input of 416 can be viewed here at   ───►   Ulam spiral (for primes)/REXX‎

clockwise[edit]

This REXX version is presented here to show the difference between a clockwise and a counter-clockwise Ulam (prime) spiral.

/*REXX program shows a    clockwise   Ulam spiral  of  primes  shown in a square matrix.*/
parse arg size init char . /*obtain optional arguments from the CL*/
if size=='' | size=="," then size=79 /*Not specified? Then use the default.*/
if init=='' | init=="," then init= 1 /* " " " " " " */
if char=='' then char="█" /* " " " " " " */
tot=size**2 /*the total number of numbers in spiral*/
/*define the upper/bottom right corners*/
uR.=0; bR.=0; do od=1 by 2 to tot; _=od**2+init; uR._=1; _=_+od; bR._=1; end /*od*/
/*define the bottom/upper left corners.*/
bL.=0; uL.=0; do ev=2 by 2 to tot; _=ev**2+init; bL._=1; _=_+ev; uL._=1; end /*ev*/
 
app=1; bigP=0; #p=0; inc=0; minR=1; maxR=1; r=1; $=0; $.=;  !.=
/*▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ construct the spiral #s.*/
do i=init for tot; r=r+inc; minR=min(minR,r); maxR=max(maxR,r)
x=isPrime(i); if x then bigP=max(bigP,i); #p=#p+x /*bigP, #primes.*/
if app then $.r=$.r || x /*append token.*/
else $.r= x || $.r /*prepend token.*/
if uR.i then do; app=1; inc=+1; iterate /*i*/; end /*advance ↓ */
if bL.i then do; app=0; inc=-1; iterate /*i*/; end /* " ↑ */
if bR.i then do; app=0; inc= 0; iterate /*i*/; end /* " ► */
if uL.i then do; app=1; inc= 0; iterate /*i*/; end /* " ◄ */
end /*i*/ /* [↓] pack two */
/*lines ──► one.*/
do j=minR to maxR by 2; jp=j+1; $=$+1 /*fold two lines*/
do k=1 for length($.j); top=substr($.j,k,1) /*the 1st line.*/
bot=word(substr($.jp,k,1) 0,1) /*the 2nd line.*/
if top then if bot then !.$= !.$'█' /*has top & bot.*/
else !.$= !.$'▀' /*has top,¬ bot.*/
else if bot then !.$= !.$'▄' /*¬ top, has bot*/
else !.$= !.$' ' /*¬ top, ¬ bot*/
end /*k*/
end /*j*/ /* [↓] show the prime spiral matrix.*/
do m=1 for $; say !.m; end /*m*/
say; say init 'is the starting point,' ,
tot 'numbers used,' #p "primes found, largest prime:" bigP
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
isPrime: procedure; parse arg x; if wordpos(x,'2 3 5 7 11 13 17 19') \==0 then return 1
if x<17 then return 0; if x// 2 ==0 then return 0
if x// 3 ==0 then return 0
/*get the last digit*/ parse var x '' -1 _; if _==5 then return 0
if x// 7 ==0 then return 0
if x//11 ==0 then return 0
if x//13 ==0 then return 0
 
do j=17 by 6 until j*j > x; if x//j ==0 then return 0
if x//(j+2) ==0 then return 0
end /*j*/
return 1

output   when using the default input:
(Shown at three-quarter size.)

▀    ▄   ▄▀    ▄ ▄         ▄ ▄    ▀ ▀   ▀    ▄  ▀  ▄  ▀   ▀       ▀    ▄   ▄
 ▄     ▄▀     ▀    ▄▀   ▀▄ ▄    ▀         ▀▄     ▄     ▄             ▄    ▀
 ▄    ▀        ▄    ▀     ▀     ▀▄ ▄▀    ▄▀ ▀▄        ▀ ▀      ▄       ▄▀
    ▀▄▀                ▄▀     ▀   ▀     ▀     ▀▄         ▄     ▄▀▄▀         ▀
    ▀ ▀▄▀   ▀     ▀▄▀▄  ▀▄    ▀ ▀      ▄    ▀▄  ▀▄       ▄         ▄▀    ▄
 ▄     ▄ ▄          ▀▄     ▄       ▄▀  ▄    ▀  ▄▀ ▀   ▀ ▀               ▀     ▀
▀          ▄▀          ▄         ▄      ▀ ▀  ▄ ▄    ▀▄   ▄ ▄▀   ▀   ▀   ▀  ▄
 ▄     ▄    ▀ ▀    ▄▀            ▄     ▄  ▀▄ ▄     ▄  ▀▄▀    ▄      ▀ ▀      ▄
           ▄ ▄▀▄       ▄     ▄  ▀▄ ▄   ▄       ▄     ▄  ▀   ▀                ▄
    ▀▄          ▀▄    ▀           ▀▄     ▄▀  ▄ ▄          ▀   ▀▄    ▀▄
▀     ▀   ▀ ▀▄ ▄    ▀   ▀ ▀   ▀     ▀           ▀▄     ▄   ▄  ▀  ▄  ▀ ▀    ▄▀
  ▀▄       ▄  ▀    ▄▀   ▀  ▄ ▄  ▀  ▄        ▀   ▀    ▄▀           ▀▄    ▀▄   ▄
    ▀▄           ▄▀           ▀  ▄▀▄   ▄▀▄    ▀    ▄    ▀▄▀     ▀       ▀   ▀ ▀
 ▄▀▄    ▀▄▀ ▀ ▀▄▀    ▄▀ ▀▄ ▄    ▀▄     ▄  ▀▄ ▄    ▀     ▀▄     ▄   ▄ ▄▀▄  ▀  ▄
   ▄   ▄     ▄ ▄       ▄ ▄▀▄ ▄▀        ▄ ▄▀ ▀  ▄     ▄ ▄   ▄ ▄   ▄       ▄   ▄
▀           ▀          ▄     ▄    ▀▄▀  ▄▀▄    ▀   ▀     ▀   ▀ ▀ ▀         ▀
▀▄▀▄▀ ▀  ▄         ▄▀▄▀     ▀  ▄▀▄     ▄   ▄▀  ▄    ▀  ▄ ▄▀      ▄  ▀    ▄▀  ▄
  ▀  ▄ ▄▀  ▄  ▀▄     ▄     ▄   ▄   ▄▀    ▄     ▄▀▄   ▄      ▀▄     ▄    ▀▄   ▄
           ▄    ▀ ▀     ▀   ▀ ▀   ▀▄▀  ▄▀   ▀ ▀   ▀   ▀ ▀   ▀   ▀ ▀       ▀
    ▀ ▀▄▀▄   ▄  ▀ ▀▄      ▀      ▄▀ ▀▄▀ ▄▄ ▄ ▄ ▄   ▄ ▄ ▄     ▄       ▄ ▄ ▄ ▄
 ▄   ▄ ▄   ▄ ▄     ▄   ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄▀ ▀▄▀      ▄    ▀    ▄ ▄    ▀    ▄▀
▀   ▀     ▀     ▀ ▀   ▀       ▀   ▀ ▀  ▄ ▄▀ ▀▄▀     ▀ ▀ ▀      ▄        ▀ ▀▄
    ▀     ▀ ▀ ▀     ▀   ▀   ▀   ▀ ▀   ▀▄ ▄    ▀▄  ▀▄▀  ▄ ▄   ▄▀▄ ▄   ▄ ▄  ▀  ▄
 ▄▀  ▄   ▄       ▄ ▄ ▄ ▄  ▀    ▄▀   ▀▄▀        ▄ ▄   ▄▀    ▄▀▄    ▀▄
     ▄          ▀▄▀    ▄▀   ▀▄   ▄    ▀  ▄▀ ▀  ▄▀ ▀ ▀          ▄      ▀    ▄
▀ ▀▄         ▄  ▀  ▄▀▄▀  ▄ ▄     ▄▀▄     ▄    ▀▄  ▀     ▀ ▀▄    ▀      ▄
 ▄▀     ▀▄         ▄▀▄    ▀   ▀      ▄   ▄▀ ▀    ▄▀  ▄ ▄           ▄    ▀     ▀
     ▄                     ▄ ▄     ▄  ▀▄  ▀ ▀   ▀  ▄     ▄    ▀ ▀ ▀  ▄▀ ▀   ▀
    ▀ ▀▄ ▄  ▀▄ ▄    ▀▄    ▀▄▀▄     ▄   ▄ ▄        ▀     ▀  ▄ ▄ ▄     ▄▀▄  ▀
     ▄       ▄ ▄   ▄   ▄  ▀     ▀   ▀▄▀  ▄▀      ▄   ▄  ▀   ▀    ▄     ▄     ▄▀
     ▄    ▀          ▄ ▄▀     ▀     ▀    ▄▀    ▄  ▀  ▄      ▀ ▀ ▀ ▀ ▀▄    ▀▄▀
▀▄ ▄    ▀▄▀  ▄▀     ▀ ▀▄   ▄     ▄▀    ▄    ▀ ▀▄  ▀▄▀▄              ▀    ▄ ▄
        ▀          ▄     ▄   ▄ ▄   ▄  ▀  ▄▀    ▄▀      ▄▀  ▄ ▄    ▀▄   ▄▀▄   ▄
    ▀ ▀    ▄▀       ▀     ▀▄ ▄  ▀      ▄  ▀       ▀        ▄     ▄   ▄▀     ▀
       ▄▀     ▀ ▀▄         ▄▀▄  ▀      ▄    ▀ ▀    ▄▀▄  ▀     ▀▄    ▀▄     ▄ ▄
 ▄▀▄       ▄ ▄      ▀    ▄    ▀▄▀              ▄  ▀  ▄ ▄▀   ▀           ▀
▀   ▀ ▀  ▄    ▀         ▀ ▀▄     ▄  ▀  ▄       ▄               ▄  ▀  ▄      ▀
▀▄▀      ▄      ▀▄   ▄      ▀     ▀▄     ▄  ▀                        ▄    ▀▄
  ▀     ▀                    ▄▀    ▄▀▄▀  ▄▀     ▀           ▀▄▀   ▀▄    ▀    ▄
      ▀     ▀     ▀             ▀     ▀   ▀     ▀       ▀                 ▀   ▀

1 is the starting point, 6241 numbers used, 811 primes found, largest prime: 6229

Ruby[edit]

It finds the number from the position ( the coordinates ).

Translation of: Python
require 'prime'
 
def cell(n, x, y, start=1)
y, x = y - n/2, x - (n - 1)/2
l = 2 * [x.abs, y.abs].max
d = y >= x ? l*3 + x + y : l - x - y
(l - 1)**2 + d + start - 1
end
 
def show_spiral(n, symbol=nil, start=1)
puts "\nN : #{n}"
format = "%#{(start + n*n - 1).to_s.size}s "
n.times do |y|
n.times do |x|
i = cell(n,x,y,start)
if symbol
print i.prime? ? symbol[0] : symbol[1]
else
print format % (i.prime? ? i : '')
end
end
puts
end
end
 
show_spiral(9)
show_spiral(25)
show_spiral(25, "# ")
Output:
N : 9
            61    59       
   37                31    
67    17          13       
          5     3    29    
      19        2 11    53 
   41     7                
71          23             
   43          47          
73                79       

N : 25
577                     571     569                     563                     557                 
                            479                                             467             463     
        401             397                             389                     383                 
    487                                     317             313     311             307     461     
                257                     251                                     241     379         
                    197             193     191                                                     
                                                139     137                     239             547 
    491             199     101              97                             181             457     
                                                 61      59             131                         
            331             103      37                      31      89     179                     
587     409     263     149      67      17              13                             373         
                                              5       3      29                                     
                        151              19           2  11      53     127     233             541 
                            107      41       7                                                     
                                 71              23                                                 
    499     337             109      43              47              83     173             449     
593             269              73                      79                     229     367         
                                    113                                             293             
                271     157                     163             167             227                 
    503             211                                             223                             
        419                     277             281     283                                         
                            347     349             353                     359             443     
599     421                                     431     433                     439                 
            509                                             521     523                             
601                     607                     613             617     619                         

N : 25
#     # #     #     #    
       #           #   # 
  #   #       #     #    
 #         #   # #   # # 
    #     #         # #  
     #   # #             
            # #     #   #
 #   # #   #       #   # 
            # #   #      
   #   # #     # # #     
# # # # # #   #       #  
           # # #         
      #   #  ## # # #   #
       # # #             
        #   #            
 # #   # #   #   # #   # 
#   #   #     #     # #  
         #           #   
    # #     #   #   #    
 #   #           #       
  #     #   # #          
       # #   #     #   # 
# #         # #     #    
   #           # #       
#     #     #   # #      

Another Version[edit]

computes the next spiral position.

require 'prime'
 
def spiral_generator(x=0, y=0)
Enumerator.new do |yielder|
yielder << [x, y] # start position
dx, dy = 0, 1 # first direction
yielder << [x+=dx, y+=dy] # second position
0.step do |i|
2.times do
i.times{ yielder << [x+=dx, y+=dy] } # going straight
dx, dy = -dy, dx # 90 degree turn
yielder << [x+=dx, y+=dy]
end
end
end
end
 
def ulam_spiral(n, start=1)
h = Hash.new(0)
position = spiral_generator
(start ... start+n*n).each do |i|
pos = position.next
h[pos] = 1 if i.prime?
end
 
chr = [[' ', '▄'], ['▀', '█']]
(xmin, xmax), (ymin, ymax) = h.keys.transpose.map(&:minmax)
(xmin..xmax).step(2).each do |x|
puts (ymin..ymax).map{|y| chr[h[[x,y]]][h[[x+1,y]]]}.join
end
end
 
[11, 122].each do |n|
puts "\nN : #{n}"
ulam_spiral(n)
end
Output:
N : 11
▀   ▀▄ ▄   
▀▄▀▄   ▄▀ ▀
   ▄▀ █▄▀▄ 
▀▄▀ ▀▄     
▀▄▀   ▀▄  ▀
  ▀        

N : 122
▄    ▀      ▄ ▄▀ ▀              ▄▀       ▀           ▀▄  ▀  ▄  ▀       ▀  ▄   ▄ ▄      ▀          ▄  ▀   ▀  ▄    ▀   ▀  ▄ 
  ▄  ▀  ▄    ▀    ▄▀   ▀ ▀            ▄   ▄▀   ▀▄▀   ▀      ▄ ▄    ▀          ▄      ▀      ▄  ▀ ▀                     ▀  
        ▄ ▄      ▀   ▀▄    ▀    ▄▀    ▄  ▀    ▄▀    ▄     ▄▀  ▄       ▄     ▄▀   ▀ ▀     ▀  ▄▀    ▄  ▀     ▀   ▀▄   ▄ ▄  ▀
▄   ▄▀   ▀    ▄                  ▀ ▀  ▄           ▄   ▄  ▀     ▀ ▀   ▀    ▄   ▄     ▄       ▄  ▀   ▀                  ▄   
 ▀▄▀                      ▄    ▀    ▄       ▄  ▀      ▄            ▀   ▀▄▀         ▀ ▀▄     ▄  ▀▄     ▄          ▀        
▄▀ ▀   ▀       ▀       ▀              ▄     ▄▀           ▀    ▄       ▄▀     ▀  ▄▀▄▀    ▄    ▀       ▀  ▄     ▄▀▄  ▀   ▀ ▀
    ▄▀         ▀    ▄     ▄  ▀▄           ▄     ▄       ▄        ▀  ▄▀  ▄    ▀▄    ▀        ▄  ▀▄     ▄  ▀     ▀▄ ▄   ▄   
  ▄▀ ▀ ▀     ▀    ▄▀         ▀ ▀▄   ▄      ▀   ▀▄ ▄     ▄   ▄      ▀   ▀                 ▀▄ ▄    ▀    ▄▀          ▄       
   ▀      ▄ ▄▀▄▀    ▄  ▀   ▀ ▀    ▄▀  ▄     ▄  ▀         ▀▄   ▄▀      ▄   ▄  ▀  ▄       ▄   ▄      ▀     ▀ ▀       ▀▄ ▄  ▀
▄    ▀▄   ▄       ▄  ▀          ▄   ▄        ▀  ▄       ▄     ▄▀ ▀        ▄   ▄  ▀ ▀▄       ▄▀    ▄      ▀▄               
           ▀            ▄▀      ▄  ▀     ▀▄▀    ▄    ▀▄▀    ▄ ▄  ▀  ▄  ▀      ▄    ▀▄▀     ▀▄     ▄   ▄▀   ▀     ▀     ▀  
▄ ▄   ▄▀▄   ▄              ▀     ▀     ▀          ▄  ▀  ▄ ▄▀  ▄▀     ▀       ▀    ▄     ▄      ▀  ▄▀   ▀     ▀   ▀       ▀
     ▀          ▄     ▄▀     ▀▄       ▄   ▄        ▀    ▄▀ ▀  ▄▀     ▀           ▀ ▀   ▀  ▄  ▀  ▄   ▄ ▄ ▄ ▄ ▄ ▄▀    ▄     
           ▀ ▀ ▀     ▀ ▀      ▄      ▀          ▄▀    ▄▀    ▄    ▀  ▄               ▄     ▄    ▀     ▀     ▀     ▀ ▀     ▀
    ▄  ▀▄       ▄  ▀ ▀▄ ▄▀ ▀    ▄ ▄▀         ▀▄▀    ▄    ▀          ▄     ▄ ▄          ▀         ▀           ▀▄    ▀▄  ▀  
▄     ▄    ▀    ▄ ▄    ▀    ▄         ▄  ▀      ▄ ▄▀ ▀      ▄          ▀▄ ▄  ▀   ▀  ▄     ▄  ▀  ▄ ▄ ▄ ▄ ▄   ▄   ▄     ▄ ▄ 
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The method of presentation of the result consulted " REXX ".

Rust[edit]

Translation of: Kotlin
Works with: Rust version 1.11.0
use std::fmt;
 
enum Direction { RIGHT, UP, LEFT, DOWN }
use ulam::Direction::*;
 
/// Indicates whether an integer is a prime number or not.
fn is_prime(a: u32) -> bool {
match a {
2 => true,
x if x <= 1 || x % 2 == 0 => false,
_ => {
let max = f64::sqrt(a as f64) as u32;
let mut x = 3;
while x <= max {
if a % x == 0 { return false; }
x += 2;
}
true
}
}
}
 
pub struct Ulam { u : Vec<Vec<String>> }
 
impl Ulam {
/// Generates one `Ulam` object.
pub fn new(n: u32, s: u32, c: char) -> Ulam {
let mut spiral = vec![vec![String::new(); n as usize]; n as usize];
let mut dir = RIGHT;
let mut y = (n / 2) as usize;
let mut x = if n % 2 == 0 { y - 1 } else { y }; // shift left for even n's
for j in s..n * n + s {
spiral[y][x] = if is_prime(j) {
if c == '\0' { format!("{:4}", j) } else { format!(" {} ", c) }
}
else { String::from(" ---") };
 
match dir {
RIGHT => if x as u32 <= n - 1 && spiral[y - 1][x].is_empty() && j > s { dir = UP; },
UP => if spiral[y][x - 1].is_empty() { dir = LEFT; },
LEFT => if x == 0 || spiral[y + 1][x].is_empty() { dir = DOWN; },
DOWN => if spiral[y][x + 1].is_empty() { dir = RIGHT; }
};
 
match dir { RIGHT => x += 1, UP => y -= 1, LEFT => x -= 1, DOWN => y += 1 };
}
Ulam { u: spiral }
}
}
 
impl fmt::Display for Ulam {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
for row in &self.u {
writeln!(f, "{}", format!("{:?}", row).replace("\"", "").replace(", ", ""));
};
writeln!(f, "")
}
}

main.rs :

mod ulam;
use ulam::*;
 
// Program entry point.
fn main() {
print!("{}", Ulam::new(9, 1, '\0'));
print!("{}", Ulam::new(9, 1, '*'));
}
Output:
[ --- --- --- ---  61 ---  59 --- ---]
[ ---  37 --- --- --- --- ---  31 ---]
[  67 ---  17 --- --- ---  13 --- ---]
[ --- --- ---   5 ---   3 ---  29 ---]
[ --- ---  19 --- ---   2  11 ---  53]
[ ---  41 ---   7 --- --- --- --- ---]
[  71 --- --- ---  23 --- --- --- ---]
[ ---  43 --- --- ---  47 --- --- ---]
[  73 --- --- --- --- ---  79 --- ---]

[ --- --- --- ---  *  ---  *  --- ---]
[ ---  *  --- --- --- --- ---  *  ---]
[  *  ---  *  --- --- ---  *  --- ---]
[ --- --- ---  *  ---  *  ---  *  ---]
[ --- ---  *  --- ---  *   *  ---  * ]
[ ---  *  ---  *  --- --- --- --- ---]
[  *  --- --- ---  *  --- --- --- ---]
[ ---  *  --- --- ---  *  --- --- ---]
[  *  --- --- --- --- ---  *  --- ---]

Scala[edit]

Translation of: Kotlin
object Ulam extends App {
generate(9)()
generate(9)('*')
 
private object Direction extends Enumeration { val RIGHT, UP, LEFT, DOWN = Value }
 
private def generate(n: Int, i: Int = 1)(c: Char = 0) {
assert(n > 1, "n > 1")
val s = new Array[Array[String]](n).transform {_ => new Array[String](n) }
 
import Direction._
var dir = RIGHT
var y = n / 2
var x = if (n % 2 == 0) y - 1 else y // shift left for even n's
for (j <- i to n * n - 1 + i) {
s(y)(x) = if (isPrime(j)) if (c == 0) "%4d".format(j) else s" $c " else " ---"
 
dir match {
case RIGHT => if (x <= n - 1 && s(y - 1)(x) == null && j > i) dir = UP
case UP => if (s(y)(x - 1) == null) dir = LEFT
case LEFT => if (x == 0 || s(y + 1)(x) == null) dir = DOWN
case DOWN => if (s(y)(x + 1) == null) dir = RIGHT
}
 
dir match {
case RIGHT => x += 1
case UP => y -= 1
case LEFT => x -= 1
case DOWN => y += 1
}
}
println("[" + s.map(_.mkString("")).reduceLeft(_ + "]\n[" + _) + "]\n")
}
 
private def isPrime(a: Int): Boolean = {
if (a == 2) return true
if (a <= 1 || a % 2 == 0) return false
val max = Math.sqrt(a.toDouble).toInt
for (n <- 3 to max by 2)
if (a % n == 0) return false
true
}
}

Sidef[edit]

Translation of: Perl
require('Imager')
 
var (n=512, start=1, file='ulam.png') = ARGV.map{.to_i}...
 
func cell(n, x, y, start) {
y -= (n >> 1)
x -= (n-1 >> 1)
var l = 2*(x.abs > y.abs ? x.abs : y.abs)
var d = (y > x  ? (l*3 + x + y) : (l - x - y))
(l-1)**2 + d + start - 1
}
 
var black = %s'Imager::Color'.new('#000000')
var white = %s'Imager::Color'.new('#FFFFFF')
 
var img = %s'Imager'.new(xsize => n, ysize => n, channels => 1)
img.box(filled => 1, color => white)
 
for y,x in (^n ~X ^n) {
var v = cell(n, x, y, start)
if (v.is_prime) {
img.setpixel(x => x, y => y, color => black)
}
}
 
img.write(file => file)

Tcl[edit]

This uses a coroutine to walk around the circle, laying glyphs every prime number of tiles. Some more elaborate, interactive Tk GUIs for playing with Ulam spirals are at Ulam Spiral and Ulam Spiral Demo on the Tcl'ers Wiki.

proc is_prime {n} {
if {$n == 1} {return 0}
if {$n in {2 3 5}} {return 1}
for {set i 2} {$i*$i <= $n} {incr i} {
if {$n % $i == 0} {return 0}
}
return 1
}
 
proc spiral {w h} {
yield [info coroutine]
set x [expr {$w / 2}]
set y [expr {$h / 2}]
set n 1
set dir 0
set steps 1
set step 1
while {1} {
yield [list $x $y]
switch $dir {
0 {incr x}
1 {incr y -1}
2 {incr x -1}
3 {incr y}
}
if {![incr step -1]} {
set dir [expr {($dir+1)%4}]
if {$dir % 2 == 0} {
incr steps
}
set step $steps
}
}
}
 
set radius 16
set side [expr {1 + 2 * $radius}]
set n [expr {$side * $side}]
set cells [lrepeat $side [lrepeat $side ""]]
set i 1
 
coroutine spin spiral $side $side
 
while {$i < $n} {
lassign [spin] y x
set c [expr {[is_prime $i] ? "\u169b" : " "}]
lset cells $x $y $c
incr i
}
 
puts [join [lmap row $cells {join $row " "}] \n]

The mark used is Unicode's OGHAM FEATHER MARK .. the closest I could find to a Tcl logo.

Output:
        ᚛   ᚛           ᚛       ᚛                       ᚛        
                              ᚛       ᚛   ᚛       ᚛              
                            ᚛       ᚛               ᚛       ᚛   ᚛
      ᚛       ᚛                       ᚛   ᚛           ᚛          
    ᚛   ᚛           ᚛   ᚛           ᚛           ᚛                
                      ᚛                       ᚛       ᚛          
᚛           ᚛       ᚛               ᚛           ᚛                
  ᚛       ᚛                   ᚛       ᚛   ᚛       ᚛   ᚛   ᚛      
᚛               ᚛           ᚛                   ᚛   ᚛       ᚛    
      ᚛           ᚛       ᚛   ᚛                               ᚛  
                                ᚛   ᚛           ᚛       ᚛       ᚛
  ᚛       ᚛       ᚛   ᚛       ᚛               ᚛       ᚛   ᚛      
                                ᚛   ᚛       ᚛                    
              ᚛       ᚛   ᚛           ᚛   ᚛   ᚛           ᚛   ᚛  
᚛   ᚛   ᚛   ᚛   ᚛   ᚛   ᚛   ᚛       ᚛               ᚛            
                              ᚛   ᚛   ᚛                       ᚛  
                    ᚛       ᚛     ᚛ ᚛   ᚛   ᚛   ᚛       ᚛   ᚛   ᚛
      ᚛               ᚛   ᚛   ᚛                                  
                        ᚛       ᚛                                
  ᚛       ᚛   ᚛       ᚛   ᚛       ᚛       ᚛   ᚛       ᚛       ᚛  
        ᚛       ᚛       ᚛           ᚛           ᚛   ᚛       ᚛    
                          ᚛                       ᚛              
                ᚛   ᚛           ᚛       ᚛       ᚛               ᚛
          ᚛       ᚛                       ᚛               ᚛      
᚛           ᚛           ᚛       ᚛   ᚛                            
                      ᚛   ᚛       ᚛           ᚛       ᚛          
᚛   ᚛   ᚛   ᚛                   ᚛   ᚛           ᚛           ᚛   ᚛
      ᚛       ᚛                       ᚛   ᚛                      
    ᚛   ᚛           ᚛           ᚛       ᚛   ᚛                    
  ᚛               ᚛                   ᚛               ᚛          
                    ᚛   ᚛       ᚛   ᚛                   ᚛        
              ᚛       ᚛           ᚛           ᚛                  
        ᚛   ᚛           ᚛                                   ᚛   

VBScript[edit]

 
Function build_spiral(n)
'declare a two dimentional array
Dim matrix()
ReDim matrix(n-1,n-1)
'determine starting point
x = (n-1)/2 : y = (n-1)/2
'set the initial iterations
x_max = 1 : y_max = 1 : count = 1
'set initial direction
dir = "R"
'populate the array
For i = 1 To n*n
l = Len(n*n)
If IsPrime(i) Then
matrix(x,y) = Right("000" & i,l)
Else
matrix(x,y) = String(l,"-")
End If
Select Case dir
Case "R"
If x_max > 0 Then
x = x + 1 : x_max = x_max - 1
Else
dir = "U" : y_max = count
y = y - 1 : y_max = y_max - 1
End If
Case "U"
If y_max > 0 Then
y = y - 1 : y_max = y_max - 1
Else
dir = "L" : count = count + 1 : x_max = count
x = x - 1 : x_max = x_max - 1
End If
Case "L"
If x_max > 0 Then
x = x - 1 : x_max = x_max - 1
Else
dir = "D" : y_max = count
y = y + 1 : y_max = y_max - 1
End If
Case "D"
If y_max > 0 Then
y = y + 1 : y_max = y_max - 1
Else
dir = "R" : count = count + 1 : x_max = count
x = x + 1 : x_max = x_max - 1
End If
End Select
Next
'print the matrix
For y = 0 To n - 1
For x = 0 To n - 1
If x = n - 1 Then
WScript.StdOut.Write matrix(x,y)
Else
WScript.StdOut.Write matrix(x,y) & vbTab
End If
Next
WScript.StdOut.WriteLine
Next
End Function
 
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
 
'test with 9
build_spiral(9)
 
Output:
--	--	--	--	61	--	59	--	--
--	37	--	--	--	--	--	31	--
67	--	17	--	--	--	13	--	--
--	--	--	05	--	03	--	29	--
--	--	19	--	--	02	11	--	53
--	41	--	07	--	--	--	--	--
71	--	--	--	23	--	--	--	--
--	43	--	--	--	47	--	--	--
73	--	--	--	--	--	79	--	--

zkl[edit]

Simulates turtle graphics, spiral by walking straight while holding left hand against the wall dropping prime breadcrumbs.

Using Extensible prime generator#zkl and the PPM class from http://rosettacode.org/wiki/Bitmap/Bresenham%27s_line_algorithm#zkl.

var primes =Utils.Generator(Import("sieve.zkl").postponed_sieve);  // lazy
var offsets=Utils.cycle( T(0,1),T(-1,0),T(0,-1),T(1,0) ); // (N,E,S,W), lazy
const BLACK=0, WHITE=0xff|ff|ff, GREEN=0x00|ff|00, EMPTY=0x080|80|80;
fcn uspiral(N){
if((M:=N).isEven) M+=1; // need odd width, height
img,p := PPM(M,M,EMPTY), primes.next(); // 2 .. 250,007: 22,045 primes
x,y,n := N/2,x,2; img[x,y]=GREEN; x+=1; // start on 2 facing "north"
while(True){
ox,oy:=offsets.next(); leftx,lefty:=offsets.peek(); // set direction
while(True){
img[x,y]=( if(n==p){ p=primes.next(); WHITE } else BLACK );
if(n==N*N) break(2); // all done
n+=1;
if(img[x+leftx,y+lefty]==EMPTY) // nothing to my left, turn left
{ x+=leftx; y+=lefty; break; }
x+=ox; y+=oy; // move in a straight line
}
}
img
}
 
uspiral(500).write(File("ulamSpiral.ppm","wb"));
Output:

A PPM image similar to that shown in Perl6 but denser. A green dot marks the center.

http://www.zenkinetic.com/Images/RosettaCode/ulamSpiral.png