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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 84 |
| 4 | 4584 |
| 5 | 469440 |
| 6 | 76982940 |
| 7 | 18391183020 |
| 8 | 6011375932800 |
| 9 | 2570927357779200 |
| 10 | 1391371186976089200 |
| 11 | 928454707768609098000 |
| 12 | 748225283395263813216000 |
| 13 | 715960677236011729384262400 |
[1,1,4,84,4584,469440,76982940,18391183020, 6011375932800,2570927357779200, 1391371186976089200,928454707768609098000, 748225283395263813216000, 715960677236011729384262400] |