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| n | a(n) |
|---|---|
| 1 | 21 |
| 2 | 51 |
| 3 | 129 |
| 4 | 339 |
| 5 | 921 |
| 6 | 2571 |
| 7 | 7329 |
| 8 | 21219 |
| 9 | 62121 |
| 10 | 183291 |
| 11 | 543729 |
| 12 | 1618899 |
| 13 | 4832121 |
| 14 | 14447211 |
| 15 | 43243329 |
| 16 | 129533379 |
| 17 | 388206921 |
| 18 | 1163834331 |
| 19 | 3489930129 |
| 20 | 10466644659 |
| 21 | 31393642521 |
| 22 | 94168344651 |
| 23 | 282479868129 |
| 24 | 847389272739 |
| 25 | 2542067154921 |
[21,51,129,339,921,2571,7329,21219,62121,183291, 543729,1618899,4832121,14447211,43243329, 129533379,388206921,1163834331,3489930129, 10466644659,31393642521,94168344651,282479868129, 847389272739,2542067154921] |