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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 13 |
| 3 | 68 |
| 4 | 560 |
| 5 | 4418 |
| 6 | 35953 |
| 7 | 304340 |
| 8 | 2636531 |
| 9 | 23265760 |
| 10 | 208241341 |
| 11 | 1884492541 |
[2,13,68,560,4418,35953,304340,2636531,23265760, 208241341,1884492541] |