The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 6 |
| 6 | 19 |
| 7 | 61 |
| 8 | 197 |
| 9 | 638 |
| 10 | 2068 |
| 11 | 6706 |
| 12 | 21747 |
| 13 | 70525 |
| 14 | 228714 |
| 15 | 741726 |
| 16 | 2405442 |
| 17 | 7800930 |
| 18 | 25298683 |
| 19 | 82044498 |
| 20 | 266073128 |
| 21 | 862884304 |
| 22 | 2798363473 |
| 23 | 9075188983 |
| 24 | 29431149984 |
| 25 | 95446231592 |
| 26 | 309535411633 |
| 27 | 1003833985448 |
[2,1,1,2,6,19,61,197,638,2068,6706,21747,70525, 228714,741726,2405442,7800930,25298683,82044498, 266073128,862884304,2798363473,9075188983, 29431149984,95446231592,309535411633, 1003833985448] |