The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 7 |
| 3 | 28 |
| 4 | 124 |
| 5 | 554 |
| 6 | 2520 |
| 7 | 11304 |
| 8 | 50958 |
| 9 | 229914 |
| 10 | 1037436 |
| 11 | 4682542 |
| 12 | 21136380 |
| 13 | 95409878 |
[1,2,7,28,124,554,2520,11304,50958,229914,1037436, 4682542,21136380,95409878] |