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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 18 |
| 5 | 120 |
| 6 | 2880 |
| 7 | 140256 |
| 8 | 20782080 |
| 9 | 9569532672 |
| 10 | 14175610675200 |
| 11 | 74559788174868480 |
[1,2,3,18,120,2880,140256,20782080,9569532672, 14175610675200,74559788174868480] |