The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 93 |
| 4 | 618 |
| 5 | 4278 |
| 6 | 30390 |
| 7 | 219810 |
| 8 | 1611105 |
| 9 | 11929395 |
| 10 | 89045079 |
| 11 | 669018837 |
| 12 | 5053759440 |
| 13 | 38350056072 |
| 14 | 292147584072 |
| 15 | 2233020788184 |
| 16 | 17117923408746 |
| 17 | 131560216858110 |
| 18 | 1013413369611606 |
| 19 | 7822237588031586 |
| 20 | 60487791859818348 |
| 21 | 468511159492134516 |
[1,3,15,93,618,4278,30390,219810,1611105,11929395, 89045079,669018837,5053759440,38350056072, 292147584072,2233020788184,17117923408746, 131560216858110,1013413369611606,7822237588031586, 60487791859818348,468511159492134516] |