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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 80 |
| 4 | 1240 |
| 5 | 30240 |
| 6 | 1071504 |
| 7 | 51996672 |
| 8 | 3307723776 |
| 9 | 266872320000 |
| 10 | 26615381760000 |
| 11 | 3214252921651200 |
| 12 | 462189467175321600 |
| 13 | 78024380924038348800 |
| 14 | 15279632043682406400000 |
| 15 | 3435553774431004262400000 |
| 16 | 879010223384483132866560000 |
| 17 | 253916900613208108255150080000 |
[1,2,9,80,1240,30240,1071504,51996672,3307723776, 266872320000,26615381760000,3214252921651200, 462189467175321600,78024380924038348800, 15279632043682406400000,3435553774431004262400000, 879010223384483132866560000, 253916900613208108255150080000] |