The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 6 |
| 6 | 21 |
| 7 | 66 |
| 8 | 170 |
| 9 | 404 |
| 10 | 984 |
| 11 | 2384 |
| 12 | 5877 |
| 13 | 14459 |
| 14 | 36720 |
| 15 | 92657 |
| 16 | 234376 |
| 17 | 597082 |
| 18 | 1525209 |
| 19 | 3913689 |
| 20 | 10076194 |
| 21 | 26016985 |
[0,0,0,1,6,21,66,170,404,984,2384,5877,14459, 36720,92657,234376,597082,1525209,3913689, 10076194,26016985] |