The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 18 |
| 6 | 69 |
| 7 | 287 |
| 8 | 1397 |
| 9 | 7634 |
| 10 | 46972 |
| 11 | 321014 |
| 12 | 2416305 |
| 13 | 19840547 |
| 14 | 176267022 |
| 15 | 1681915809 |
| 16 | 17127587977 |
| 17 | 185127766583 |
[0,0,1,2,6,18,69,287,1397,7634,46972,321014, 2416305,19840547,176267022,1681915809,17127587977, 185127766583] |