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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 21 |
| 5 | 224 |
| 6 | 3075 |
| 7 | 50364 |
| 8 | 958881 |
| 9 | 20786744 |
| 10 | 505233987 |
| 11 | 13603353928 |
| 12 | 401819713273 |
| 13 | 12917450788956 |
| 14 | 448922610588491 |
| 15 | 16770152528046332 |
| 16 | 670096317408222529 |
| 17 | 28517474585339343408 |
| 18 | 1287722135213121579203 |
[0,0,1,2,21,224,3075,50364,958881,20786744, 505233987,13603353928,401819713273,12917450788956, 448922610588491,16770152528046332, 670096317408222529,28517474585339343408, 1287722135213121579203] |