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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 4 |
| 4 | -18 |
| 5 | 110 |
| 6 | -810 |
| 7 | 7040 |
| 8 | -70280 |
| 9 | 792200 |
| 10 | -9945000 |
| 11 | 137550400 |
| 12 | -2077719600 |
| 13 | 34026132400 |
| 14 | -600433397200 |
| 15 | 11356783360000 |
| 16 | -229193571984000 |
| 17 | 4915556301968000 |
| 18 | -111644265232656000 |
| 19 | 2676908220027392000 |
[0,1,-1,4,-18,110,-810,7040,-70280,792200, -9945000,137550400,-2077719600,34026132400, -600433397200,11356783360000,-229193571984000, 4915556301968000,-111644265232656000, 2676908220027392000] |