title: Find row of pyramid based on index?
body: <p>Given a pyramid like:</p>
  
  <pre><code>      0
       1 2
      3 4 5
     6 7 8 9
       ...
  </code></pre>
  
  <p>and given the index of the pyramid <code>i</code> where <code>i</code> represents the <code>i</code>th number of the pyramid, is there a way to find the index of the row to which the <code>i</code>th element belongs? (e.g. if <code>i = 6,7,8,9</code>, it is in the 3rd row, starting from row 0)</p>