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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 2 |
| 4 | 18 |
| 5 | 792 |
| 6 | 209880 |
| 7 | 389117520 |
| 8 | 5771780174160 |
| 9 | 770509566129663360 |
| 10 | 1028600220910021528728960 |
| 11 | 15104551945968674840127424147200 |
| 12 | 2661646219535110627933754465838408595200 |
[1,2,18,792,209880,389117520,5771780174160, 770509566129663360,1028600220910021528728960, 15104551945968674840127424147200, 2661646219535110627933754465838408595200] |