The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 25 |
| 6 | 102 |
| 7 | 456 |
| 8 | 2218 |
| 9 | 11605 |
| 10 | 64647 |
| 11 | 379349 |
| 12 | 2320555 |
| 13 | 14658240 |
| 14 | 94843284 |
| 15 | 624544847 |
| 16 | 4164947151 |
| 17 | 28025750099 |
| 18 | 189783308469 |
| 19 | 1290899153376 |
| 20 | 8808076870934 |
| 21 | 60230644078721 |
| 22 | 412493027114619 |
| 23 | 2827998455493193 |
[0,1,2,7,25,102,456,2218,11605,64647,379349, 2320555,14658240,94843284,624544847,4164947151, 28025750099,189783308469,1290899153376, 8808076870934,60230644078721,412493027114619, 2827998455493193] |