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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 135 |
| 4 | 1215 |
| 5 | 12636 |
| 6 | 147987 |
| 7 | 1917999 |
| 8 | 27162540 |
| 9 | 416236401 |
| 10 | 6848207775 |
| 11 | 120206639790 |
| 12 | 2239278203277 |
| 13 | 44074161731151 |
| 14 | 913065539247018 |
| 15 | 19843943547060315 |
| 16 | 451135755042249987 |
| 17 | 10701182793462338052 |
| 18 | 264250529777677991751 |
| 19 | 6779171511882363638619 |
| 20 | 180350988089950776032172 |
[1,3,18,135,1215,12636,147987,1917999,27162540, 416236401,6848207775,120206639790,2239278203277, 44074161731151,913065539247018,19843943547060315, 451135755042249987,10701182793462338052, 264250529777677991751,6779171511882363638619, 180350988089950776032172] |