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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 6 |
| 3 | 10 |
| 4 | 259200 |
| 5 | 87178291200 |
| 6 | 202741834014720 |
| 7 | 484725313854093312000000 |
| 8 | 4438779300500903005519872000000 |
| 9 | 346902756482949716983678260882702336000000000 |
[1,3,6,10,259200,87178291200,202741834014720, 484725313854093312000000, 4438779300500903005519872000000, 346902756482949716983678260882702336000000000] |