The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 38 |
| 6 | 211 |
| 7 | 1381 |
| 8 | 10451 |
| 9 | 89575 |
| 10 | 857352 |
| 11 | 9063435 |
| 12 | 104876888 |
| 13 | 1318452296 |
| 14 | 17893281148 |
| 15 | 260730668151 |
| 16 | 4059948975491 |
| 17 | 67279154450986 |
| 18 | 1182190856781604 |
| 19 | 21954973054515490 |
| 20 | 429690186924088871 |
[1,1,1,3,9,38,211,1381,10451,89575,857352,9063435, 104876888,1318452296,17893281148,260730668151, 4059948975491,67279154450986,1182190856781604, 21954973054515490,429690186924088871] |