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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 42 |
| 4 | 20592 |
| 5 | 20957398 |
| 6 | 38833756515 |
| 7 | 117650546564305 |
| 8 | 543403955513408885 |
[0,1,42,20592,20957398,38833756515, 117650546564305,543403955513408885] |