| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 9 |
| 2 | 60 |
| 3 | 344 |
| 4 | 1794 |
| 5 | 8754 |
| 6 | 40636 |
| 7 | 181380 |
| 8 | 784251 |
| 9 | 3302451 |
| 10 | 13598280 |
| 11 | 54922860 |
| 12 | 218131380 |
| 13 | 853586100 |
| 14 | 3296508840 |
| 15 | 12581531064 |
| 16 | 47510175861 |
| 17 | 177681098205 |
| 18 | 658665849636 |
| 19 | 2422018974096 |
| 20 | 8840103322374 |
| 21 | 32044237392726 |
[1,9,60,344,1794,8754,40636,181380,784251,3302451, 13598280,54922860,218131380,853586100,3296508840, 12581531064,47510175861,177681098205,658665849636, 2422018974096,8840103322374,32044237392726] |