The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 15 |
| 4 | 53 |
| 5 | 204 |
| 6 | 457 |
| 7 | 12199 |
| 8 | 110580 |
| 9 | 765920 |
| 10 | 29631246 |
| 11 | 733709898 |
| 12 | 22329951066 |
[1,2,6,15,53,204,457,12199,110580,765920,29631246, 733709898,22329951066] |