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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 16 |
| 5 | 72 |
| 6 | 432 |
| 7 | 2880 |
| 8 | 23040 |
| 9 | 201600 |
| 10 | 2016000 |
| 11 | 21772800 |
| 12 | 261273600 |
| 13 | 3353011200 |
| 14 | 46942156800 |
| 15 | 697426329600 |
| 16 | 11158821273600 |
| 17 | 188305108992000 |
| 18 | 3389491961856000 |
| 19 | 64023737057280000 |
| 20 | 1280474741145600000 |
[1,2,4,16,72,432,2880,23040,201600,2016000, 21772800,261273600,3353011200,46942156800, 697426329600,11158821273600,188305108992000, 3389491961856000,64023737057280000, 1280474741145600000] |