The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 71 |
| 6 | 264 |
| 7 | 1015 |
| 8 | 4002 |
| 9 | 16094 |
| 10 | 65758 |
| 11 | 272208 |
| 12 | 1139182 |
| 13 | 4811807 |
| 14 | 20487096 |
| 15 | 87832558 |
| 16 | 378846620 |
| 17 | 1642851797 |
| 18 | 7158220968 |
| 19 | 31323340342 |
| 20 | 137595355130 |
| 21 | 606533278416 |
| 22 | 2682157911032 |
| 23 | 11895267124841 |
| 24 | 52895679368820 |
| 25 | 235792891885786 |
| 26 | 1053475824902774 |
[1,1,2,6,20,71,264,1015,4002,16094,65758,272208, 1139182,4811807,20487096,87832558,378846620, 1642851797,7158220968,31323340342,137595355130, 606533278416,2682157911032,11895267124841, 52895679368820,235792891885786,1053475824902774] |