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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 8 |
| 4 | 240 |
| 5 | 18264 |
| 6 | 2845440 |
| 7 | 792731520 |
| 8 | 359935488000 |
| 9 | 248962406889600 |
[1,1,8,240,18264,2845440,792731520,359935488000, 248962406889600] |