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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 21 |
| 4 | 552 |
| 5 | 19560 |
| 6 | 920160 |
| 7 | 55974240 |
| 8 | 4293596160 |
| 9 | 406306575360 |
| 10 | 46556342784000 |
| 11 | 6357567896064000 |
| 12 | 1020650937901056000 |
| 13 | 190386526063878144000 |
| 14 | 40844355820490686464000 |
| 15 | 9987985777548364185600000 |
| 16 | 2762125829379285162393600000 |
| 17 | 857790151281459139077734400000 |
[0,1,21,552,19560,920160,55974240,4293596160, 406306575360,46556342784000,6357567896064000, 1020650937901056000,190386526063878144000, 40844355820490686464000,9987985777548364185600000, 2762125829379285162393600000, 857790151281459139077734400000] |