The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 46 |
| 6 | 260 |
| 7 | 1731 |
| 8 | 13220 |
| 9 | 114177 |
| 10 | 1100259 |
| 11 | 11702761 |
| 12 | 136177584 |
| 13 | 1720789475 |
| 14 | 23465311032 |
| 15 | 343446825119 |
| 16 | 5370259447316 |
| 17 | 89341588987179 |
| 18 | 1575660751228445 |
| 19 | 29364586727439203 |
| 20 | 576613703011533457 |
[1,0,1,2,9,46,260,1731,13220,114177,1100259, 11702761,136177584,1720789475,23465311032, 343446825119,5370259447316,89341588987179, 1575660751228445,29364586727439203, 576613703011533457] |