input  [1, 5, 2, 4, 6, 3, 2, 6]

divide [1, 5, 2, 4, 6, 3, 2, 6] -> [1, 5, 2, 4] [6, 3, 2, 6]
  divide [1, 5, 2, 4] -> [1, 5] [2, 4]
    divide [1, 5] -> [1] [5]
    merge  -> [1, 5]
    divide [2, 4] -> [2] [4]
    merge  -> [2, 4]
  merge  -> [1, 2, 4, 5]
  divide [6, 3, 2, 6] -> [6, 3] [2, 6]
    divide [6, 3] -> [6] [3]
    merge  -> [3, 6]
    divide [2, 6] -> [2] [6]
    merge  -> [2, 6]
  merge  -> [2, 3, 6, 6]
merge  -> [1, 2, 2, 3, 4, 5, 6, 6]

sorted [1, 2, 2, 3, 4, 5, 6, 6]
comparisons for n = 8: 16

n          comparisons      n lg n    ratio
---------------------------------------------
16         47               64          0.734
64         307              384         0.799
256        1725             2048        0.842
1024       8962             10240       0.875
4096       43970            49152       0.895
65536      965956           1048576     0.921
