The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 15 |
| 4 | 99 |
| 5 | 630 |
| 6 | 4599 |
| 7 | 34099 |
| 8 | 261603 |
| 9 | 2036026 |
| 10 | 16075980 |
| 11 | 128214840 |
| 12 | 1031495768 |
[1,4,15,99,630,4599,34099,261603,2036026,16075980, 128214840,1031495768] |