G'day thanos1983,

Here's a recursive function that, I believe, achieves what you're after.

#!/usr/bin/env perl -l

use strict;
use warnings;

use constant BASE => ord('A') - 1;
use constant MAX  => ord('Z') - BASE;

my @tests = (
    0 .. 3, 24 .. 28, 
    26**2+24 .. 26**2+28,
    26**3+26**2+24 .. 26**3+26**2+28,
);

print "IN: $_ OUT: ", translate($_) for @tests;

sub translate {
    my ($in, $out) = @_;

    $out ||= [];

    return join '', @$out if $in == 0;

    my $mod = $in % MAX || MAX;

    unshift @$out, chr $mod + BASE;

    my $new_in = ($in - $mod) / MAX;

    translate($new_in, $out);
}
[download]

Output:

IN: 0 OUT: 
IN: 1 OUT: A
IN: 2 OUT: B
IN: 3 OUT: C
IN: 24 OUT: X
IN: 25 OUT: Y
IN: 26 OUT: Z
IN: 27 OUT: AA
IN: 28 OUT: AB
IN: 700 OUT: ZX
IN: 701 OUT: ZY
IN: 702 OUT: ZZ
IN: 703 OUT: AAA
IN: 704 OUT: AAB
IN: 18276 OUT: ZZX
IN: 18277 OUT: ZZY
IN: 18278 OUT: ZZZ
IN: 18279 OUT: AAAA
IN: 18280 OUT: AAAB
[download]

"I am not posting the code here as it is irrelevant and will only consume space, ..."

A cutdown version might have provided some context. Without that, I don't know exactly how you'd implement this solution. You'll probably want some validation of the input.