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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | -1 |
| 3 | -4 |
| 4 | 18 |
| 5 | -118 |
| 6 | 495 |
| 7 | -3336 |
| 8 | 16492 |
| 9 | -124390 |
| 10 | 697995 |
| 11 | -5665356 |
| 12 | 31847574 |
| 13 | -230282830 |
| 14 | 297803779 |
| 15 | 15399702624 |
| 16 | -527666397480 |
| 17 | 11555528032498 |
| 18 | -238917247672905 |
| 19 | 4947107036570988 |
| 20 | -102644658064599590 |
[0,2,-1,-4,18,-118,495,-3336,16492,-124390,697995, -5665356,31847574,-230282830,297803779, 15399702624,-527666397480,11555528032498, -238917247672905,4947107036570988, -102644658064599590] |