| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 17 |
| 6 | 94 |
| 7 | 609 |
| 8 | 4552 |
| 9 | 38476 |
| 10 | 362881 |
| 11 | 3779006 |
| 12 | 43077462 |
| 13 | 533580649 |
| 14 | 7136963118 |
| 15 | 102529626260 |
| 16 | 1574596837316 |
| 17 | 25744424249914 |
| 18 | 446484648899818 |
| 19 | 8187058430845388 |
| 20 | 158263924457447255 |
| 21 | 3216829977408052830 |
[1,1,1,4,17,94,609,4552,38476,362881,3779006, 43077462,533580649,7136963118,102529626260, 1574596837316,25744424249914,446484648899818, 8187058430845388,158263924457447255, 3216829977408052830] |