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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 14 |
| 5 | 78 |
| 6 | 504 |
| 7 | 3720 |
| 8 | 30960 |
| 9 | 256320 |
| 10 | 2656080 |
| 11 | 30078720 |
| 12 | 369774720 |
| 13 | 4906137600 |
| 14 | 69894316800 |
| 15 | 1064341555200 |
| 16 | 16190733081600 |
| 17 | 279499828608000 |
| 18 | 5100017213491200 |
| 19 | 98087346669312000 |
| 20 | 1983334021853184000 |
| 21 | 42063950934061056000 |
| 22 | 933754193111900160000 |
[1,0,1,4,14,78,504,3720,30960,256320,2656080, 30078720,369774720,4906137600,69894316800, 1064341555200,16190733081600,279499828608000, 5100017213491200,98087346669312000, 1983334021853184000,42063950934061056000, 933754193111900160000] |