The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 20 |
| 3 | 115 |
| 4 | 633 |
| 5 | 4234 |
| 6 | 29949 |
| 7 | 225630 |
| 8 | 1762579 |
| 9 | 14176573 |
| 10 | 116718282 |
| 11 | 979244657 |
| 12 | 8343503219 |
[4,20,115,633,4234,29949,225630,1762579,14176573, 116718282,979244657,8343503219] |