I'm working on a script that generate some Excel documents and I need to convert a number into its column name equivalent. For example:

```
1 => A
2 => B
27 => AA
28 => AB
14558 => UMX
```

I have already written an algorithm to do so, but I'd like to know whether are simpler or faster ways to do it:

```
function numberToColumnName($number){
$abc = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
$abc_len = strlen($abc);
$result_len = 1; // how much characters the column's name will have
$pow = 0;
while( ( $pow += pow($abc_len, $result_len) ) < $number ){
$result_len++;
}
$result = "";
$next = false;
// add each character to the result...
for($i = 1; $i<=$result_len; $i++){
$index = ($number % $abc_len) - 1; // calculate the module
// sometimes the index should be decreased by 1
if( $next || $next = false ){
$index--;
}
// this is the point that will be calculated in the next iteration
$number = floor($number / strlen($abc));
// if the index is negative, convert it to positive
if( $next = ($index < 0) ) {
$index = $abc_len + $index;
}
$result = $abc[$index].$result; // concatenate the letter
}
return $result;
}
```

Do you know a better way to do it? Maybe something to keep it simpler? or a performance improvement?

### Edit

ircmaxell's implementation works pretty fine. But, I'm going to add this nice short one:

```
function num2alpha($n)
{
for($r = ""; $n >= 0; $n = intval($n / 26) - 1)
$r = chr($n%26 + 0x41) . $r;
return $r;
}
```

Here's a nice simple recursive function (Based on zero indexed numbers, meaning 0 == A, 1 == B, etc)...

And if you want it one indexed (1 == A, etc):

Tested with numbers from 0 to 10000...