エラトステネスの篩

sieve_of_eratosthenes.pl

use strict;
use warnings;

my $n = $ARGV[0] || 1000;
my $nums = [2..$n];
my $p_index = 0;

while (1) {
  my $p = $nums->[$p_index++];
  last if $p > sqrt($n);
  @$nums = grep { ($_ == $p) or ($_ % $p) } @$nums;
}

$" = "\n";
print "1\n@$nums";