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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 20 |
| 4 | 94 |
| 5 | 854 |
| 6 | 7638 |
| 7 | 77678 |
| 8 | 823184 |
| 9 | 11711952 |
| 10 | 162710640 |
| 11 | 2405290392 |
| 12 | 40661618688 |
| 13 | 701353671264 |
| 14 | 13592382983424 |
| 15 | 280431464804640 |
| 16 | 5835146351362560 |
| 17 | 130171240155651840 |
| 18 | 3168997587241864704 |
| 19 | 77082927941097660672 |
| 20 | 2037627154674197591040 |
| 21 | 56017463733173686947840 |
[1,1,3,20,94,854,7638,77678,823184,11711952, 162710640,2405290392,40661618688,701353671264, 13592382983424,280431464804640,5835146351362560, 130171240155651840,3168997587241864704, 77082927941097660672,2037627154674197591040, 56017463733173686947840] |