| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 3 |
| 5 | 13 |
| 6 | 68 |
| 7 | 426 |
| 8 | 3103 |
| 9 | 25751 |
| 10 | 239484 |
| 11 | 2466678 |
| 12 | 27873457 |
| 13 | 342843515 |
| 14 | 4559818741 |
| 15 | 65205407995 |
| 16 | 997642742322 |
| 17 | 16261576699845 |
| 18 | 281325276907304 |
| 19 | 5148252567403659 |
| 20 | 99361274550890614 |
| 21 | 2017033873383079454 |
[1,1,1,1,3,13,68,426,3103,25751,239484,2466678, 27873457,342843515,4559818741,65205407995, 997642742322,16261576699845,281325276907304, 5148252567403659,99361274550890614, 2017033873383079454] |