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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 6 |
| 4 | 12 |
| 5 | 20 |
| 6 | 60 |
| 7 | 1680 |
| 8 | 4032 |
| 9 | 181440 |
| 10 | 907200 |
| 11 | 2851200 |
| 12 | 17107200 |
| 13 | 62270208 |
| 14 | 242161920 |
| 15 | 29059430400 |
| 16 | 232475443200 |
| 17 | 1077840691200 |
| 18 | 277159034880 |
| 19 | 52660216627200 |
| 20 | 283555012608000 |
| 21 | 65501207912448000 |
| 22 | 720513287036928000 |
[1,1,1,6,12,20,60,1680,4032,181440,907200,2851200, 17107200,62270208,242161920,29059430400, 232475443200,1077840691200,277159034880, 52660216627200,283555012608000,65501207912448000, 720513287036928000] |