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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 20 |
| 3 | 1680 |
| 4 | 369240 |
| 5 | 167472864 |
| 6 | 135960447600 |
| 7 | 179637314905576 |
| 8 | 360796550854271920 |
[1,20,1680,369240,167472864,135960447600, 179637314905576,360796550854271920] |