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Here is my ASCII version of Ulam's spiral, ie. spiralling outwards not inwards.

use strict; use warnings; use Math::Prime::XS 'sieve_primes'; my $n = shift; my %primes = map { $_ => 'O' } sieve_primes $n; my @spiral; my $o = 1 + int( sqrt( $n )/2 ); my ( $x, $y ) = ( $o, $o ); # starting point my ( $xs, $ys ) = ( 1, 0 ); # initial direction my $flip = 1; # change of direction indicator my $m = 1; # length of current lag for my $i ( 1..$n ) { $spiral[$y][$x] = $primes{ $i }//' '; $x += $xs; $y += $ys; ($xs, $ys) = ( ( $flip=1-$flip ) and $m++ ) ? ($ys, 0) : (0, -$xs) + unless $i%$m; } $spiral[$o][$o] = 'X'; print join '', map { $_//' '} @$_, "\n" for @spiral;

In reply to Re: Spiraling integers by hdb
in thread Spiraling integers by Elijah

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