| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 15 |
| 5 | 76 |
| 6 | 455 |
| 7 | 3186 |
| 8 | 25487 |
| 9 | 229384 |
| 10 | 2293839 |
| 11 | 25232230 |
| 12 | 302786759 |
| 13 | 3936227868 |
| 14 | 55107190151 |
| 15 | 826607852266 |
| 16 | 13225725636255 |
| 17 | 224837335816336 |
| 18 | 4047072044694047 |
| 19 | 76894368849186894 |
| 20 | 1537887376983737879 |
| 21 | 32295634916658495460 |
| 22 | 710503968166486900119 |
[0,1,1,4,15,76,455,3186,25487,229384,2293839, 25232230,302786759,3936227868,55107190151, 826607852266,13225725636255,224837335816336, 4047072044694047,76894368849186894, 1537887376983737879,32295634916658495460, 710503968166486900119] |