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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 15 |
| 3 | 987 |
| 4 | 453837 |
| 5 | 1296261759 |
| 6 | 23643209345079 |
| 7 | 2745117942652795617 |
[0,15,987,453837,1296261759,23643209345079, 2745117942652795617] |