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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 15 |
| 3 | 111 |
| 4 | 649 |
| 5 | 3495 |
| 6 | 18189 |
| 7 | 93231 |
| 8 | 474479 |
| 9 | 2406621 |
| 10 | 12187137 |
| 11 | 61668609 |
| 12 | 311938233 |
| 13 | 1577602849 |
| 14 | 7977940187 |
| 15 | 40342860995 |
| 16 | 204001993697 |
| 17 | 1031568839407 |
| 18 | 5216271035257 |
| 19 | 26376744398811 |
| 20 | 133377264694375 |
[1,15,111,649,3495,18189,93231,474479,2406621, 12187137,61668609,311938233,1577602849,7977940187, 40342860995,204001993697,1031568839407, 5216271035257,26376744398811,133377264694375] |