The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 0 |
| 7 | 1 |
| 8 | 3 |
| 9 | 9 |
| 10 | 25 |
| 11 | 69 |
| 12 | 201 |
| 13 | 620 |
| 14 | 1923 |
| 15 | 6339 |
| 16 | 22238 |
| 17 | 82443 |
| 18 | 333723 |
| 19 | 1490051 |
| 20 | 7241421 |
[0,0,0,0,0,0,1,3,9,25,69,201,620,1923,6339,22238, 82443,333723,1490051,7241421] |