title: When working with Mergesort, quicksort etc, is O(n log n) base 2, or base 10?
body: <p>I'm a little confused about big O notations.</p>
  
  <p>Let's say I'm working with an array of 16 elements and trying to do a QuickSort.</p>
  
  <p>A QuickSort's Average case is O(n log n) and its worst case is O(n^2)</p>
  
  <p>I assumed it would be log base 2 since we're working with computers (binary).  But I've also heard you could use base 10 and get the same complexity. </p>
  
  <p>I figured it would be 16*log2*16 == 16 * 4 = 64 comparisons at O(n log n).</p>
  
  <p>At O(n^2) == 16^2 ==  256 comparisons at its worst case.</p>
  
  <p>Do I have the right idea?  And as a general rule, should I be using base 10 or base 2? </p>