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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 8 |
| 4 | 50 |
| 5 | 214 |
| 6 | 2086 |
| 7 | 11976 |
| 8 | 162816 |
| 9 | 1143576 |
| 10 | 20472504 |
| 11 | 165910128 |
| 12 | 3785092032 |
| 13 | 33908109936 |
| 14 | 967508478192 |
| 15 | 9252123203712 |
| 16 | 327062428940160 |
| 17 | 3236057604910080 |
| 18 | 141403289873955840 |
| 19 | 1404243298160352000 |
| 20 | 76168955916831029760 |
| 21 | 735206146073008508160 |
[1,1,3,8,50,214,2086,11976,162816,1143576, 20472504,165910128,3785092032,33908109936, 967508478192,9252123203712,327062428940160, 3236057604910080,141403289873955840, 1404243298160352000,76168955916831029760, 735206146073008508160] |