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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 6 |
| 4 | -12 |
| 5 | -60 |
| 6 | 720 |
| 7 | -2520 |
| 8 | -20160 |
| 9 | 362880 |
| 10 | -1814400 |
| 11 | -19958400 |
| 12 | 479001600 |
| 13 | -3113510400 |
| 14 | -43589145600 |
| 15 | 1307674368000 |
| 16 | -10461394944000 |
| 17 | -177843714048000 |
| 18 | 6402373705728000 |
| 19 | -60822550204416000 |
| 20 | -1216451004088320000 |
| 21 | 51090942171709440000 |
| 22 | -562000363888803840000 |
[1,-1,6,-12,-60,720,-2520,-20160,362880,-1814400, -19958400,479001600,-3113510400,-43589145600, 1307674368000,-10461394944000,-177843714048000, 6402373705728000,-60822550204416000, -1216451004088320000,51090942171709440000, -562000363888803840000] |