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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 13 |
| 4 | 48 |
| 5 | 381 |
| 6 | 3120 |
| 7 | 26923 |
| 8 | 255696 |
| 9 | 3158137 |
| 10 | 40008240 |
| 11 | 519979791 |
| 12 | 7942304040 |
| 13 | 122856625477 |
| 14 | 2131578891624 |
| 15 | 39647280625891 |
| 16 | 750423985762080 |
| 17 | 15134456564892273 |
| 18 | 334165931467245216 |
| 19 | 7422976578858122647 |
| 20 | 177254117413133743800 |
| 21 | 4454974632071621551741 |
[1,1,2,13,48,381,3120,26923,255696,3158137, 40008240,519979791,7942304040,122856625477, 2131578891624,39647280625891,750423985762080, 15134456564892273,334165931467245216, 7422976578858122647,177254117413133743800, 4454974632071621551741] |