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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 6 |
| 5 | 14 |
| 6 | 42 |
| 7 | 3810 |
| 8 | 318990 |
| 9 | 13243560 |
| 10 | 1108809240 |
| 11 | 1719507048 |
| 12 | 25330080090 |
| 13 | 271984504290 |
[1,2,3,6,14,42,3810,318990,13243560,1108809240, 1719507048,25330080090,271984504290] |