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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 1 |
| 3 | 1 |
| 4 | 3 |
| 5 | 15 |
| 6 | 91 |
| 7 | 647 |
| 8 | 5245 |
| 9 | 48287 |
| 10 | 625817 |
| 11 | 36494225 |
| 12 | 6862660263 |
| 13 | 1568810412647 |
| 14 | 390685537439419 |
| 15 | 106288930934710885 |
[2,1,1,3,15,91,647,5245,48287,625817,36494225, 6862660263,1568810412647,390685537439419, 106288930934710885] |