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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 24 |
| 5 | 240 |
| 6 | 2040 |
| 7 | 17640 |
| 8 | 182616 |
| 9 | 2340576 |
| 10 | 34907520 |
| 11 | 567732000 |
| 12 | 9811675104 |
| 13 | 179804319552 |
| 14 | 3507724531584 |
| 15 | 72964001073600 |
| 16 | 1614757714491456 |
| 17 | 37860036000293376 |
| 18 | 936291898320463872 |
| 19 | 24333527620574701056 |
| 20 | 662723505438520771584 |
| 21 | 18871765275000834201600 |
[1,0,0,0,24,240,2040,17640,182616,2340576, 34907520,567732000,9811675104,179804319552, 3507724531584,72964001073600,1614757714491456, 37860036000293376,936291898320463872, 24333527620574701056,662723505438520771584, 18871765275000834201600] |