The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 7 |
| 3 | 30 |
| 4 | 141 |
| 5 | 698 |
| 6 | 3571 |
| 7 | 18686 |
| 8 | 99385 |
| 9 | 535122 |
| 10 | 2908863 |
| 11 | 15932766 |
| 12 | 87809541 |
| 13 | 486421770 |
| 14 | 2706138987 |
| 15 | 15110359038 |
| 16 | 84637982961 |
| 17 | 475381503266 |
| 18 | 2676447372535 |
| 19 | 15100548901790 |
| 20 | 85357620588541 |
| 21 | 483304834607322 |
[1,2,7,30,141,698,3571,18686,99385,535122,2908863, 15932766,87809541,486421770,2706138987, 15110359038,84637982961,475381503266, 2676447372535,15100548901790,85357620588541, 483304834607322] |