get_natural_numbers.pl

#!/usr/bin/env perl 

use Modern::Perl;

my @natural = separator(10_000_000);
say scalar @natural;

sub separator {
    my $number = shift;
    my %hash = map { $_ => 1 } 1..$number;

    for ( my $i = 2; $i * $i <= $number; $i++ ) {
        if ( $hash{ $i } ) {
            for ( my $composite = $i * $i; $composite <= $number; $composite += $i ) {
                delete $hash{$composite};
            }
        }
    }

    return sort { $a <=> $b } keys %hash;

}