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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 0 |
| 5 | 60 |
| 6 | 1080 |
| 7 | 840 |
| 8 | 80640 |
| 9 | 982800 |
| 10 | 5292000 |
| 11 | 249812640 |
| 12 | 2854051200 |
| 13 | 46711304640 |
| 14 | 1595483809920 |
| 15 | 22132648137600 |
| 16 | 649972279756800 |
| 17 | 19151306772998400 |
| 18 | 377272414943424000 |
| 19 | 14076577060273728000 |
| 20 | 407012458114918656000 |
| 21 | 11429334092933569612800 |
[1,0,0,6,0,60,1080,840,80640,982800,5292000, 249812640,2854051200,46711304640,1595483809920, 22132648137600,649972279756800,19151306772998400, 377272414943424000,14076577060273728000, 407012458114918656000,11429334092933569612800] |