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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 510 |
| 4 | 6745200 |
| 5 | 19038823123320 |
| 6 | 19549762329157865925120 |
| 7 | 11131011767163918530071193512089600 |
| 8 | 4977434038774545402380656971924547417738384800000 |
[1,1,4,510,6745200,19038823123320, 19549762329157865925120, 11131011767163918530071193512089600, 4977434038774545402380656971924547417738384800000] |