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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 18 |
| 5 | 180 |
| 6 | 2700 |
| 7 | 56700 |
| 8 | 1587600 |
| 9 | 57153600 |
| 10 | 2571912000 |
| 11 | 141455160000 |
| 12 | 9336040560000 |
| 13 | 728211163680000 |
| 14 | 66267215894880000 |
| 15 | 6958057668962400000 |
| 16 | 834966920275488000000 |
| 17 | 113555501157466368000000 |
| 18 | 17373991677092354304000000 |
| 19 | 2970952576782792585984000000 |
[1,1,3,18,180,2700,56700,1587600,57153600, 2571912000,141455160000,9336040560000, 728211163680000,66267215894880000, 6958057668962400000,834966920275488000000, 113555501157466368000000, 17373991677092354304000000, 2970952576782792585984000000] |