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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 3 |
| 5 | 15 |
| 6 | 30 |
| 7 | 180 |
| 8 | 3780 |
| 9 | 291060 |
| 10 | 3783780 |
| 11 | 70982929216999800 |
[1,1,1,3,3,15,30,180,3780,291060,3783780, 70982929216999800] |