The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 18 |
| 5 | 68 |
| 6 | 313 |
| 7 | 1592 |
| 8 | 9187 |
| 9 | 57451 |
| 10 | 384450 |
| 11 | 2703970 |
| 12 | 19769311 |
[1,2,6,18,68,313,1592,9187,57451,384450,2703970, 19769311] |