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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 3 |
| 4 | 6 |
| 5 | 20 |
| 6 | 450 |
| 7 | 3024 |
| 8 | 21840 |
| 9 | 449280 |
| 10 | 5690160 |
| 11 | 68579280 |
| 12 | 1491462720 |
| 13 | 27798076800 |
| 14 | 485405784864 |
| 15 | 11821894207200 |
| 16 | 285057334598400 |
| 17 | 6578025489584640 |
| 18 | 183420564173141760 |
| 19 | 5342163886869062400 |
| 20 | 152988752430721267200 |
| 21 | 4897735504358795965440 |
[0,0,0,3,6,20,450,3024,21840,449280,5690160, 68579280,1491462720,27798076800,485405784864, 11821894207200,285057334598400,6578025489584640, 183420564173141760,5342163886869062400, 152988752430721267200,4897735504358795965440] |