1 by orig = 1 (1 calls to sub)
1 by tail = 1 (2 calls to sub)

2 by orig = 1 (1 calls to sub)
2 by tail = 1 (3 calls to sub)

3 by orig = 2 (3 calls to sub)
3 by tail = 2 (4 calls to sub)

4 by orig = 3 (5 calls to sub)
4 by tail = 3 (5 calls to sub)

5 by orig = 5 (9 calls to sub)
5 by tail = 5 (6 calls to sub)

10 by orig = 55 (109 calls to sub)
10 by tail = 55 (11 calls to sub)

15 by orig = 610 (1219 calls to sub)
15 by tail = 610 (16 calls to sub)

25 by orig = 75025 (150049 calls to sub)
25 by tail = 75025 (26 calls to sub)