| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 4 |
| 6 | 14 |
| 7 | 49 |
| 8 | 234 |
| 9 | 1476 |
| 10 | 15405 |
| 11 | 307536 |
| 12 | 12651788 |
| 13 | 1044977929 |
| 14 | 167207997404 |
| 15 | 50838593828724 |
| 16 | 29156171171238607 |
| 17 | 31484900549777534887 |
| 18 | 64064043979274771429379 |
| 19 | 246064055301339083624989655 |
| 20 | 1788069981480210465772374023323 |
| 21 | 24641385885409824180500407923934750 |
[1,1,1,1,2,4,14,49,234,1476,15405,307536,12651788, 1044977929,167207997404,50838593828724, 29156171171238607,31484900549777534887, 64064043979274771429379, 246064055301339083624989655, 1788069981480210465772374023323, 24641385885409824180500407923934750] |