数字からExcelの行番号?(AEとか)を得る

num_to_alphabet.php

<?php
function getAlphabetByNum($num, $carryNum=null) {
  $alphabetCount = 26;
  if ($num < $alphabetCount) {
    if ($carryNum === null) return chr(97 + $num);
    $carryAlphabet = ($carryNum > $alphabetCount) ? getAlphabetByNum($carryNum) :
                     chr(97 + $carryNum);
    return $carryAlphabet . chr(97 + $num);
  } 
  $carryNum  = ($carryNum === null) ? 0 : $carryNum + 1;
  return getAlphabetByNum($num - $alphabetCount, $carryNum);
}