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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 0 |
| 5 | 120 |
| 6 | 2160 |
| 7 | 4620 |
| 8 | 322560 |
| 9 | 4656960 |
| 10 | 51408000 |
| 11 | 2225805120 |
| 12 | 36404121600 |
| 13 | 935298524160 |
| 14 | 34191689051520 |
| 15 | 769760181590400 |
| 16 | 29060360301772800 |
| 17 | 1049180522277888000 |
| 18 | 33363257180449996800 |
| 19 | 1488084913957723361280 |
| 20 | 58703745178055577600000 |
[1,0,0,6,0,120,2160,4620,322560,4656960,51408000, 2225805120,36404121600,935298524160, 34191689051520,769760181590400,29060360301772800, 1049180522277888000,33363257180449996800, 1488084913957723361280,58703745178055577600000] |