gistfile1.txt

use strict;
use warnings;

my @results;

sub functional_number {
    my $num = shift;

    if( $results[$num] ) {
        return $results[$num];
    }

    return 0 if $num == 0;
    return 1 if $num == 1 || $num == 2;
    $results[$num] = functional_number($num - 1) + functional_number($num - 2);
}

use Data::Dumper;
warn Dumper [ map { functional_number $_ } (0..50) ];