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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | -1 |
| 2 | 4 |
| 3 | 7 |
| 4 | 120 |
| 5 | 1373 |
| 6 | 21028 |
| 7 | 373931 |
| 8 | 7670736 |
| 9 | 178064281 |
| 10 | 4615519884 |
| 11 | 132139421423 |
| 12 | 4141235867992 |
| 13 | 141016013784917 |
| 14 | 5184372688776180 |
| 15 | 204668397165154867 |
| 16 | 8635388122600110240 |
| 17 | 387787185320578895537 |
| 18 | 18467131524896950511644 |
[1,-1,4,7,120,1373,21028,373931,7670736,178064281, 4615519884,132139421423,4141235867992, 141016013784917,5184372688776180, 204668397165154867,8635388122600110240, 387787185320578895537,18467131524896950511644] |