Versuchs hiermit:
function to_26($zahl) {
$chars = Array(
0,1,2,3,4,5,6,7,8,9,
'A','B','C','D','E',
'F','G','H','I','J',
'K','L','M','N','O',
'P','Q','R','S','T',
'U','V','W','X','Y','Z'
);
$a = 1;
while($zahl >= $a) {
$a *= 26;
}
while($a != 1) {
$a /= 26;
$b = $zahl / $a;
$zahl %= $a;
$result .= $chars[$b];
}
return $result;
}