The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 10 |
| 5 | 15 |
| 6 | 49 |
| 7 | 147 |
| 8 | 407 |
| 9 | 1084 |
| 10 | 3010 |
| 11 | 8756 |
| 12 | 25145 |
| 13 | 73424 |
| 14 | 215375 |
| 15 | 631828 |
| 16 | 1870092 |
| 17 | 5562131 |
| 18 | 16584139 |
| 19 | 49630873 |
| 20 | 148917071 |
| 21 | 448088250 |
[0,0,4,10,15,49,147,407,1084,3010,8756,25145, 73424,215375,631828,1870092,5562131,16584139, 49630873,148917071,448088250] |