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| n | a(n) |
|---|---|
| 4 | 54 |
| 5 | 20 |
| 6 | 3552 |
| 7 | 11364 |
| 8 | 2742240 |
| 9 | 56271108 |
| 10 | 23882769984 |
| 11 | 990946452040 |
| 12 | 760348893638560 |
[54,20,3552,11364,2742240,56271108,23882769984, 990946452040,760348893638560] |