title: Sum of decimal digit
body: <p>The following was a programming interview practice question.<br>
  What is the smart way to handle this?  </p>
  
  <p>A number M is stored in an array in the reverse order. For example, the number 274 is stored in the following array:</p>
  
  <pre><code>A[0]= 4 A[1]=7 A[2]=2
  </code></pre>
  
  <p>Write a function that given the array A representing some number, returns the sum of the digits of a decimal representation of the number M * 17. Array size can be very large (more than 2,000,000 elements).</p>