n | a(n) |
---|---|
1 | 0 |
2 | 1 |
3 | 2 |
4 | 6 |
5 | 18 |
6 | 72 |
7 | 321 |
8 | 1680 |
9 | 9852 |
10 | 64168 |
11 | 457659 |
12 | 3543785 |
13 | 29578097 |
14 | 264623046 |
15 | 2525897073 |
16 | 25622275565 |
17 | 275257714175 |
18 | 3122190896616 |
19 | 37290114445901 |
20 | 467812869356846 |
[0,1,2,6,18,72,321,1680,9852,64168,457659,3543785, 29578097,264623046,2525897073,25622275565, 275257714175,3122190896616,37290114445901, 467812869356846] |