The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 24 |
| 6 | 68 |
| 7 | 200 |
| 8 | 652 |
| 9 | 2203 |
| 10 | 7794 |
| 11 | 28182 |
| 12 | 103979 |
| 13 | 387931 |
| 14 | 1461376 |
| 15 | 5541033 |
| 16 | 21126533 |
| 17 | 80897892 |
| 18 | 310938666 |
| 19 | 1198917744 |
| 20 | 4635816939 |
| 21 | 17969766349 |
| 22 | 69812201957 |
| 23 | 271768139230 |
| 24 | 1059903743280 |
| 25 | 4140631641752 |
| 26 | 16200937633453 |
| 27 | 63479707135804 |
| 28 | 249060516700509 |
[1,2,4,10,24,68,200,652,2203,7794,28182,103979, 387931,1461376,5541033,21126533,80897892, 310938666,1198917744,4635816939,17969766349, 69812201957,271768139230,1059903743280, 4140631641752,16200937633453,63479707135804, 249060516700509] |