I'm confused, this sounds like if you just need to calculate modulo 26 to be able to transform 27 to AA.

Am I missing something?

edit

Something like this?

while ($n) {
    $i = $n % 26;
    unshift @vector, $i;
    $n -= $i;
    $n /= 26;
} 

print map { chr(64+$_) } @vector;
[download]

Untested!