The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 0 |
| 4 | 2 |
| 5 | 10 |
| 6 | 37 |
| 7 | 121 |
| 8 | 725 |
| 9 | 5160 |
| 10 | 31794 |
| 11 | 279136 |
| 12 | 2137531 |
| 13 | 21305316 |
| 14 | 213311303 |
| 15 | 2457648287 |
| 16 | 30357607661 |
| 17 | 387013387043 |
| 18 | 5245097770693 |
[0,1,0,2,10,37,121,725,5160,31794,279136,2137531, 21305316,213311303,2457648287,30357607661, 387013387043,5245097770693] |