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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 15 |
| 3 | 509 |
| 4 | 65409 |
| 5 | 33488029 |
| 6 | 68583014753 |
| 7 | 561830980890331 |
| 8 | 18410060198369526671 |
[1,15,509,65409,33488029,68583014753, 561830980890331,18410060198369526671] |