The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 3 |
| 6 | 9 |
| 7 | 23 |
| 8 | 77 |
| 9 | 415 |
| 10 | 2809 |
| 11 | 21039 |
| 12 | 202829 |
| 13 | 2557861 |
| 14 | 41110329 |
| 15 | 812468577 |
| 16 | 20241517719 |
| 17 | 638623731453 |
| 18 | 25413793552471 |
[1,1,1,1,3,9,23,77,415,2809,21039,202829,2557861, 41110329,812468577,20241517719,638623731453, 25413793552471] |