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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 100 |
| 5 | 794 |
| 6 | 11268 |
| 7 | 264083 |
| 8 | 10769600 |
| 9 | 713951303 |
| 10 | 72018421871 |
| 11 | 10336964079379 |
| 12 | 1993158443643362 |
[2,6,18,100,794,11268,264083,10769600,713951303, 72018421871,10336964079379,1993158443643362] |