   n   sum of costs   closed form   3n-floor(lg n)-2   amortized
       1              1             1                  1      1.0000
       2              3             3                  3      1.5000
       3              4             4                  6      1.3333
       4              8             8                  8      2.0000
       5              9             9                 11      1.8000
       8             19            19                 19      2.3750
      16             42            42                 42      2.6250
     100            220           220                292      2.2000
    1000           2013          2013               2989      2.0130
    1024           3060          3060               3060      2.9883
  100000         231054        231054             299982      2.3105
 1000000        2048555       2048555            2999979      2.0486

The first two numeric columns agree at every checkpoint, so the
closed form is right; the third is never smaller than the first,
so the bound holds; the last column stays below 3, so the
amortized cost is O(1).
