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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 56 |
| 5 | 448 |
| 6 | 4928 |
| 7 | 64064 |
| 8 | 896896 |
| 9 | 14350336 |
| 10 | 272656384 |
| 11 | 5725784064 |
| 12 | 125967249408 |
| 13 | 3149181235200 |
| 14 | 81878712115200 |
| 15 | 2292603939225600 |
| 16 | 71070722115993600 |
| 17 | 2274263107711795200 |
| 18 | 79599208769912832000 |
| 19 | 2945170724486774784000 |
| 20 | 111916487530497441792000 |
| 21 | 4588575988750395113472000 |
[1,1,2,8,56,448,4928,64064,896896,14350336, 272656384,5725784064,125967249408,3149181235200, 81878712115200,2292603939225600,71070722115993600, 2274263107711795200,79599208769912832000, 2945170724486774784000,111916487530497441792000, 4588575988750395113472000] |