  i  actual  charged  credit   2j+k+2
  1       1        3       2        2
  2       2        3       3        3
  3       1        3       5        5
  4       4        3       4        4
  5       1        3       6        6
  6       1        3       8        8
  7       1        3      10       10
  8       8        3       5        5
  9       1        3       7        7
 10       1        3       9        9
 11       1        3      11       11
 12       1        3      13       13
 13       1        3      15       15
 14       1        3      17       17
 15       1        3      19       19
 16      16        3       6        6
 17       1        3       8        8

closed form 2j+k+2 agrees for every i up to 1000000: yes
lowest credit ever seen = 0  (the accounting method needs this to be >= 0)
total actual cost = 2048555, total charged = 3000000, so 3n is indeed an upper bound.
