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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 0 |
| 5 | 60 |
| 6 | 2520 |
| 7 | 1680 |
| 8 | 181440 |
| 9 | 6138720 |
| 10 | 18295200 |
| 11 | 1444988160 |
| 12 | 46443196800 |
| 13 | 357015859200 |
| 14 | 25016537145600 |
| 15 | 818965321574400 |
| 16 | 12259854032025600 |
| 17 | 815066633667686400 |
| 18 | 28461465853402982400 |
| 19 | 691667282863484928000 |
| 20 | 45198900807076912896000 |
| 21 | 1739192274792359202816000 |
| 22 | 60318174486002275287244800 |
[1,0,0,6,0,60,2520,1680,181440,6138720,18295200, 1444988160,46443196800,357015859200, 25016537145600,818965321574400,12259854032025600, 815066633667686400,28461465853402982400, 691667282863484928000,45198900807076912896000, 1739192274792359202816000, 60318174486002275287244800] |