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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 576 |
| 5 | 80640 |
| 6 | 505958400 |
| 7 | 30739709952000 |
| 8 | 55019078005712486400 |
[1,2,6,576,80640,505958400,30739709952000, 55019078005712486400] |