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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 6 |
| 3 | 15 |
| 4 | 36 |
| 5 | 225 |
| 6 | 561 |
| 7 | 1225 |
| 8 | 11935 |
| 9 | 11781 |
| 10 | 27405 |
| 11 | 220780 |
| 12 | 203841 |
| 13 | 3368925 |
| 14 | 4921840 |
| 15 | 7316001 |
| 16 | 33631521 |
| 17 | 142629201 |
| 18 | 879207616 |
| 19 | 1383958576 |
| 20 | 3800798001 |
| 21 | 12524486976 |
| 22 | 181285005825 |
| 23 | 118037679760 |
| 24 | 239764947345 |
| 25 | 738541591425 |
| 26 | 1289707733601 |
| 27 | 1559439365121 |
[3,6,15,36,225,561,1225,11935,11781,27405,220780, 203841,3368925,4921840,7316001,33631521,142629201, 879207616,1383958576,3800798001,12524486976, 181285005825,118037679760,239764947345, 738541591425,1289707733601,1559439365121] |