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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 1680 |
| 4 | 108972864000 |
| 5 | 137047310902965380295426048000000 |
| 6 | 5507245320567889066989296412116383715402149139520190633628554443368693760000000000000 |
[2,6,1680,108972864000, 137047310902965380295426048000000, 55072453205678890669892964121163837154021491395201\ 90633628554443368693760000000000000] |