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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | -2 |
| 3 | 9 |
| 4 | -28 |
| 5 | 0 |
| 6 | 1200 |
| 7 | -16464 |
| 8 | 167904 |
| 9 | -1393200 |
| 10 | 7429240 |
| 11 | 43124400 |
| 12 | -2404571904 |
| 13 | 55590286752 |
| 14 | -1027511503200 |
| 15 | 16489054310400 |
| 16 | -222885864448000 |
| 17 | 1994839594780032 |
| 18 | 14489184835474272 |
| 19 | -1470395490046560000 |
| 20 | 54581408106475622400 |
| 21 | -1608207353670788640000 |
[1,0,-2,9,-28,0,1200,-16464,167904,-1393200, 7429240,43124400,-2404571904,55590286752, -1027511503200,16489054310400,-222885864448000, 1994839594780032,14489184835474272, -1470395490046560000,54581408106475622400, -1608207353670788640000] |