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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 100 |
| 5 | 794 |
| 6 | 11268 |
| 7 | 252987 |
| 8 | 8945756 |
| 9 | 446201625 |
| 10 | 30067026570 |
| 11 | 2590515855716 |
| 12 | 274837925289083 |
[2,6,18,100,794,11268,252987,8945756,446201625, 30067026570,2590515855716,274837925289083] |