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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 12 |
| 6 | 33 |
| 7 | 83 |
| 8 | 273 |
| 9 | 937 |
| 10 | 3983 |
| 11 | 18871 |
| 12 | 103697 |
| 13 | 628245 |
| 14 | 4161652 |
| 15 | 29372754 |
| 16 | 218035754 |
[1,2,6,12,33,83,273,937,3983,18871,103697,628245, 4161652,29372754,218035754] |