The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 640 |
| 7 | 3924 |
| 8 | 25536 |
| 9 | 205708 |
| 10 | 1739900 |
| 11 | 16259796 |
| 12 | 161820114 |
| 13 | 1804403590 |
| 14 | 21159038910 |
| 15 | 264205593296 |
| 16 | 3464634505962 |
[1,2,6,24,120,640,3924,25536,205708,1739900, 16259796,161820114,1804403590,21159038910, 264205593296,3464634505962] |