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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | -3 |
| 4 | 12 |
| 5 | -70 |
| 6 | 370 |
| 7 | -2436 |
| 8 | 20048 |
| 9 | -175176 |
| 10 | 1679368 |
| 11 | -18271000 |
| 12 | 216489416 |
| 13 | -2751576048 |
| 14 | 37874200208 |
| 15 | -560956931640 |
| 16 | 8845252164864 |
| 17 | -148215651070272 |
| 18 | 2635014886145472 |
| 19 | -49474969983055872 |
| 20 | 977864639612813440 |
[1,0,2,-3,12,-70,370,-2436,20048,-175176,1679368, -18271000,216489416,-2751576048,37874200208, -560956931640,8845252164864,-148215651070272, 2635014886145472,-49474969983055872, 977864639612813440] |