title: Algorithm for digit summing?
body: <p>I'm searching for an algorithm for Digit summing. Let me outline the basic principle:</p>
  
  <p>Say you have a number: <code>18268</code>.</p>
  
  <pre><code>1 + 8 + 2 + 6 + 8 = 25
  
  2 + 5 = 7
  </code></pre>
  
  <p>And 7 is our final number. It's basically adding each number of the whole number until we get down to a single (also known as a 'core') digit. It's often used by numerologists.</p>
  
  <p>I'm searching for an algorithm (doesn't have to be language in-specific) for this. I have searched Google for the last hour with terms such as <code>digit sum algorithm</code> and whatnot but got no suitable results.</p>