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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 31 |
| 3 | 180 |
| 4 | 1141 |
| 5 | 7589 |
| 6 | 46988 |
| 7 | 307547 |
| 8 | 2021039 |
| 9 | 13090390 |
| 10 | 85028181 |
| 11 | 551562559 |
| 12 | 3578528548 |
| 13 | 23237970485 |
| 14 | 150848706421 |
| 15 | 979297967866 |
| 16 | 6357554112195 |
| 17 | 41269666346783 |
| 18 | 267909267230378 |
| 19 | 1739184952510823 |
| 20 | 11290199883542271 |
[3,31,180,1141,7589,46988,307547,2021039,13090390, 85028181,551562559,3578528548,23237970485, 150848706421,979297967866,6357554112195, 41269666346783,267909267230378,1739184952510823, 11290199883542271] |