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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 96 |
| 5 | 840 |
| 6 | 8640 |
| 7 | 105840 |
| 8 | 1491840 |
| 9 | 23587200 |
| 10 | 413683200 |
| 11 | 7983360000 |
| 12 | 168129561600 |
| 13 | 3835844812800 |
| 14 | 94239732787200 |
| 15 | 2480658276096000 |
| 16 | 69651967537152000 |
| 17 | 2077925954936832000 |
| 18 | 65637135231123456000 |
[1,1,2,12,96,840,8640,105840,1491840,23587200, 413683200,7983360000,168129561600,3835844812800, 94239732787200,2480658276096000,69651967537152000, 2077925954936832000,65637135231123456000] |