>> hw019
  1 + 1 + 1 = 3
  1 + 1 + 3 = 5
  1 + 3 + 5 = 9
  3 + 5 + 9 = 17
  5 + 9 + 17 = 31
  9 + 17 + 31 = 57
  17 + 31 + 57 = 105
  31 + 57 + 105 = 193
  57 + 105 + 193 = 355
  105 + 193 + 355 = 653