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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 420 |
| 2 | 81496800 |
| 3 | 6988909668048000 |
| 4 | 264339188251171547754240000 |
| 5 | 4409145118315866486641282521305984000000 |
| 6 | 32432910584848683243891703579686352553931989191680000000 |
[1,420,81496800,6988909668048000, 264339188251171547754240000, 4409145118315866486641282521305984000000, 32432910584848683243891703579686352553931989191680\ 000000] |