The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 13 |
| 4 | 52 |
| 5 | 264 |
| 6 | 1585 |
| 7 | 11099 |
| 8 | 88794 |
| 9 | 799147 |
| 10 | 7991477 |
| 11 | 87906255 |
| 12 | 1054875070 |
| 13 | 13713375910 |
| 14 | 191987262753 |
| 15 | 2879808941305 |
| 16 | 46076943060891 |
| 17 | 783308032035156 |
| 18 | 14099544576632824 |
| 19 | 267891346956023663 |
| 20 | 5357826939120473260 |
[2,4,13,52,264,1585,11099,88794,799147,7991477, 87906255,1054875070,13713375910,191987262753, 2879808941305,46076943060891,783308032035156, 14099544576632824,267891346956023663, 5357826939120473260] |