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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 6 |
| 4 | 36 |
| 5 | 240 |
| 6 | 1800 |
| 7 | 15120 |
| 8 | 141120 |
| 9 | 1451520 |
| 10 | 16329600 |
| 11 | 199584000 |
| 12 | 2634508800 |
| 13 | 37362124800 |
| 14 | 566658892800 |
| 15 | 9153720576000 |
| 16 | 156920924160000 |
| 17 | 2845499424768000 |
| 18 | 54420176498688000 |
| 19 | 1094805903679488000 |
| 20 | 23112569077678080000 |
| 21 | 510909421717094400000 |
[1,6,36,240,1800,15120,141120,1451520,16329600, 199584000,2634508800,37362124800,566658892800, 9153720576000,156920924160000,2845499424768000, 54420176498688000,1094805903679488000, 23112569077678080000,510909421717094400000] |