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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 126 |
| 5 | 1667 |
| 6 | 31966 |
| 7 | 828678 |
| 8 | 27535826 |
| 9 | 1128945382 |
| 10 | 55473589278 |
| 11 | 3193471420236 |
| 12 | 211517309562652 |
[1,3,15,126,1667,31966,828678,27535826,1128945382, 55473589278,3193471420236,211517309562652] |