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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 20 |
| 3 | 204 |
| 4 | 2784 |
| 5 | 47520 |
| 6 | 973440 |
| 7 | 23264640 |
| 8 | 635443200 |
| 9 | 19525847040 |
| 10 | 666654105600 |
| 11 | 25037094297600 |
| 12 | 1025783842406400 |
| 13 | 45529186384281600 |
| 14 | 2176249118883840000 |
| 15 | 111452688851632128000 |
| 16 | 6088372509440212992000 |
[1,3,20,204,2784,47520,973440,23264640,635443200, 19525847040,666654105600,25037094297600, 1025783842406400,45529186384281600, 2176249118883840000,111452688851632128000, 6088372509440212992000] |