The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 16 |
| 4 | 52 |
| 5 | 152 |
| 6 | 512 |
| 7 | 1568 |
| 8 | 5392 |
| 9 | 16992 |
| 10 | 59232 |
| 11 | 190336 |
| 12 | 669952 |
| 13 | 2183680 |
| 14 | 7742464 |
| 15 | 25512448 |
| 16 | 90974464 |
| 17 | 302368256 |
| 18 | 1083175424 |
| 19 | 3625435136 |
| 20 | 13036688384 |
| 21 | 43889186816 |
| 22 | 158323564544 |
| 23 | 535639556096 |
| 24 | 1937483350016 |
| 25 | 6582584115200 |
| 26 | 23865932414976 |
| 27 | 81381420826624 |
| 28 | 295661476642816 |
[1,2,6,16,52,152,512,1568,5392,16992,59232,190336, 669952,2183680,7742464,25512448,90974464, 302368256,1083175424,3625435136,13036688384, 43889186816,158323564544,535639556096, 1937483350016,6582584115200,23865932414976, 81381420826624,295661476642816] |