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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 28 |
| 4 | 182 |
| 5 | 1640 |
| 6 | 19220 |
| 7 | 278224 |
| 8 | 4809942 |
| 9 | 96598622 |
| 10 | 2208156512 |
| 11 | 56580566908 |
| 12 | 1605518324884 |
| 13 | 49963000166616 |
| 14 | 1691615823420800 |
| 15 | 61897541544248720 |
| 16 | 2433873670903995990 |
| 17 | 102341746590575878628 |
| 18 | 4582360425862350559350 |
| 19 | 217661837260679635780356 |
[1,2,6,28,182,1640,19220,278224,4809942,96598622, 2208156512,56580566908,1605518324884, 49963000166616,1691615823420800,61897541544248720, 2433873670903995990,102341746590575878628, 4582360425862350559350,217661837260679635780356] |