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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 120 |
| 5 | 718 |
| 6 | 4994 |
| 7 | 39556 |
| 8 | 351320 |
| 9 | 3456742 |
| 10 | 37314126 |
| 11 | 438366374 |
| 12 | 5567209930 |
| 13 | 75995663398 |
| 14 | 1109556555434 |
| 15 | 17252609166736 |
| 16 | 284620418911180 |
| 17 | 4965138989585412 |
| 18 | 91317809653363376 |
| 19 | 1765937111915469414 |
[2,6,24,120,718,4994,39556,351320,3456742, 37314126,438366374,5567209930,75995663398, 1109556555434,17252609166736,284620418911180, 4965138989585412,91317809653363376, 1765937111915469414] |