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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 15 |
| 3 | 81 |
| 4 | 435 |
| 5 | 2337 |
| 6 | 12555 |
| 7 | 67449 |
| 8 | 362355 |
| 9 | 1946673 |
| 10 | 10458075 |
| 11 | 56183721 |
| 12 | 301834755 |
| 13 | 1621541217 |
| 14 | 8711375595 |
| 15 | 46799960409 |
| 16 | 251422553235 |
| 17 | 1350712686993 |
| 18 | 7256408541435 |
| 19 | 38983468081161 |
| 20 | 209430157488675 |
| 21 | 1125117723605697 |
[3,15,81,435,2337,12555,67449,362355,1946673, 10458075,56183721,301834755,1621541217,8711375595, 46799960409,251422553235,1350712686993, 7256408541435,38983468081161,209430157488675, 1125117723605697] |