secs          speedup
   n    1 node   4 nodes     ratio
  17      0.46      0.82      0.56
  21      0.65      0.88      0.74
  25      4.03      1.82      2.21
  29     67.08     19.16      3.50
  31    285.76     77.77      3.67
  32    615.60    158.79      3.88
  33  43832.15    332.56    131.80
  34      0.00    736.54      0.00