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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 21 |
| 5 | 144 |
| 6 | 1765 |
| 7 | 21552 |
| 8 | 340137 |
| 9 | 5845760 |
| 10 | 116495721 |
| 11 | 2550320640 |
| 12 | 62023290109 |
| 13 | 1642735460352 |
| 14 | 47321500546125 |
| 15 | 1469008742856704 |
| 16 | 48962556079079505 |
| 17 | 1742660440701861888 |
| 18 | 65993849612007279697 |
| 19 | 2648999558505185280000 |
| 20 | 112360563741545020804581 |
[1,0,1,2,21,144,1765,21552,340137,5845760, 116495721,2550320640,62023290109,1642735460352, 47321500546125,1469008742856704,48962556079079505, 1742660440701861888,65993849612007279697, 2648999558505185280000,112360563741545020804581] |