The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 21 |
| 5 | 183 |
| 6 | 1918 |
| 7 | 22908 |
| 8 | 290511 |
| 9 | 3844666 |
| 10 | 52453581 |
| 11 | 733300683 |
| 12 | 10458157796 |
| 13 | 151676284707 |
| 14 | 2231506564296 |
[1,1,1,4,21,183,1918,22908,290511,3844666, 52453581,733300683,10458157796,151676284707, 2231506564296] |