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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 52 |
| 6 | 334 |
| 7 | 2866 |
| 8 | 31902 |
| 9 | 439510 |
| 10 | 7372150 |
| 11 | 147351714 |
| 12 | 3460114654 |
| 13 | 94073798158 |
| 14 | 2926942982790 |
| 15 | 103161703653178 |
| 16 | 4084845678671086 |
| 17 | 180433041383154870 |
| 18 | 8836346732709839206 |
| 19 | 477142911818397135058 |
| 20 | 28265453383985064929934 |
[1,1,2,4,12,52,334,2866,31902,439510,7372150, 147351714,3460114654,94073798158,2926942982790, 103161703653178,4084845678671086, 180433041383154870,8836346732709839206, 477142911818397135058,28265453383985064929934] |