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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 360 |
| 3 | 9000 |
| 4 | 283500 |
| 5 | 11113200 |
| 6 | 533433600 |
| 7 | 30862944000 |
| 8 | 2121827400000 |
| 9 | 171160743600000 |
| 10 | 16020645600960000 |
| 11 | 1722947613266880000 |
| 12 | 211061082625192800000 |
| 13 | 29223842209642080000000 |
| 14 | 4542220046298654720000000 |
| 15 | 787620956028186728448000000 |
[1,18,360,9000,283500,11113200,533433600, 30862944000,2121827400000,171160743600000, 16020645600960000,1722947613266880000, 211061082625192800000,29223842209642080000000, 4542220046298654720000000, 787620956028186728448000000] |