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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 17 |
| 5 | 91 |
| 6 | 587 |
| 7 | 4327 |
| 8 | 35604 |
| 9 | 323316 |
| 10 | 3210600 |
| 11 | 34574453 |
| 12 | 400893066 |
| 13 | 4975247460 |
| 14 | 65755573847 |
| 15 | 921535225267 |
| 16 | 13643496840808 |
| 17 | 212688569520955 |
| 18 | 3480978391442106 |
| 19 | 59657975022473437 |
| 20 | 1068151956803180295 |
| 21 | 19937983367649562025 |
| 22 | 387243759600707804811 |
| 23 | 7812456801157894913964 |
[1,0,1,4,17,91,587,4327,35604,323316,3210600, 34574453,400893066,4975247460,65755573847, 921535225267,13643496840808,212688569520955, 3480978391442106,59657975022473437, 1068151956803180295,19937983367649562025, 387243759600707804811,7812456801157894913964] |