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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | 40 |
| 6 | 540 |
| 7 | 3528 |
| 8 | 25200 |
| 9 | 324000 |
| 10 | 3648960 |
| 11 | 41690880 |
| 12 | 622274400 |
| 13 | 9573033600 |
| 14 | 150465579264 |
| 15 | 2705877820800 |
| 16 | 51819600268800 |
| 17 | 1028013655818240 |
| 18 | 22086154437442560 |
| 19 | 504188626820659200 |
| 20 | 11997041025160396800 |
| 21 | 301999960230701322240 |
[0,0,0,6,12,40,540,3528,25200,324000,3648960, 41690880,622274400,9573033600,150465579264, 2705877820800,51819600268800,1028013655818240, 22086154437442560,504188626820659200, 11997041025160396800,301999960230701322240] |