The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 6 |
| 4 | 21 |
| 5 | 100 |
| 6 | 645 |
| 7 | 4256 |
| 8 | 34153 |
| 9 | 302352 |
| 10 | 2966505 |
| 11 | 32245664 |
| 12 | 380114493 |
| 13 | 4879093440 |
| 14 | 67244074989 |
| 15 | 996485811712 |
| 16 | 15717842398417 |
| 17 | 264232448010496 |
| 18 | 4694489063253585 |
| 19 | 88283645811756544 |
| 20 | 1744673430747688805 |
[1,1,1,6,21,100,645,4256,34153,302352,2966505, 32245664,380114493,4879093440,67244074989, 996485811712,15717842398417,264232448010496, 4694489063253585,88283645811756544, 1744673430747688805] |