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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 36 |
| 6 | 252 |
| 7 | 2772 |
| 8 | 52668 |
| 9 | 1211364 |
| 10 | 35129556 |
| 11 | 1089016236 |
| 12 | 44649665676 |
| 13 | 2098534286772 |
| 14 | 417608323067628 |
| 15 | 88115356167269508 |
| 16 | 24760415083002731748 |
| 17 | 7948093241643876891108 |
| 18 | 4140956578896459860267268 |
[1,2,4,12,36,252,2772,52668,1211364,35129556, 1089016236,44649665676,2098534286772, 417608323067628,88115356167269508, 24760415083002731748,7948093241643876891108, 4140956578896459860267268] |