gistfile1.txt

my @codes = 'a'..'z' X~ 'a'..'z';

sub simple($n) {
    @codes[$n % +@codes];
}

my $last = @codes[* - 1];

sub full($n) {
    my $prefix = $last x ($n div +@codes);
    my $value = simple($n);
    $prefix ~ $value;
}

say full(1);
say full(10);
say full(100);
say full(1000);
say full(10000);