title: is there a way to extend LETTERS past 26 characters e.g., AA, AB, AC...?
body: <p>I use LETTERS most of the time for my factors but today I tried to go beyond 26 characters:</p>
  
  <pre><code>LETTERS[1:32]
  </code></pre>
  
  <p>Expecting there to be an automatic recursive factorization AA, AB, AC... But was disappointed. Is this simply a limitation of LETTERS or is there a way to get what I'm looking for using another function?</p>