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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 12 |
| 5 | 54 |
| 6 | 288 |
| 7 | 1800 |
| 8 | 12960 |
| 9 | 105840 |
| 10 | 967680 |
| 11 | 9797760 |
| 12 | 108864000 |
| 13 | 1317254400 |
| 14 | 17244057600 |
| 15 | 242853811200 |
| 16 | 3661488230400 |
| 17 | 58845346560000 |
| 18 | 1004293914624000 |
| 19 | 18140058832896000 |
| 20 | 345728180109312000 |
| 21 | 6933770723303424000 |
[1,2,3,12,54,288,1800,12960,105840,967680,9797760, 108864000,1317254400,17244057600,242853811200, 3661488230400,58845346560000,1004293914624000, 18140058832896000,345728180109312000, 6933770723303424000] |