| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 3 |
| 5 | 11 |
| 6 | 32 |
| 7 | 152 |
| 8 | 625 |
| 9 | 3152 |
| 10 | 16154 |
| 11 | 90993 |
| 12 | 539181 |
| 13 | 3398803 |
| 14 | 22561791 |
| 15 | 157493522 |
| 16 | 1151863409 |
| 17 | 8803760900 |
| 18 | 70149141443 |
| 19 | 581461668973 |
| 20 | 5004153572628 |
[1,1,1,3,11,32,152,625,3152,16154,90993,539181, 3398803,22561791,157493522,1151863409,8803760900, 70149141443,581461668973,5004153572628] |