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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 15 |
| 3 | 27 |
| 4 | 531 |
| 5 | 1635 |
| 6 | 28161 |
| 7 | 90393 |
| 8 | 1539207 |
| 9 | 4956927 |
| 10 | 84335553 |
| 11 | 271665969 |
| 12 | 4621740687 |
| 13 | 14888070495 |
| 14 | 253283346081 |
| 15 | 815905965057 |
| 16 | 13880597644287 |
| 17 | 44713811014239 |
| 18 | 760693546670625 |
| 19 | 2450435395047009 |
| 20 | 41688023124390687 |
[0,15,27,531,1635,28161,90393,1539207,4956927, 84335553,271665969,4621740687,14888070495, 253283346081,815905965057,13880597644287, 44713811014239,760693546670625,2450435395047009, 41688023124390687] |