The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 90 |
| 4 | 594 |
| 5 | 4158 |
| 6 | 30294 |
| 7 | 227205 |
| 8 | 1741905 |
| 9 | 13586859 |
| 10 | 107459703 |
| 11 | 859677624 |
| 12 | 6943550040 |
| 13 | 56540336040 |
| 14 | 463630755528 |
| 15 | 3824953733106 |
| 16 | 31724616256938 |
| 17 | 264371802141150 |
| 18 | 2212374554760150 |
| 19 | 18583946259985260 |
| 20 | 156636118477018620 |
[1,3,15,90,594,4158,30294,227205,1741905,13586859, 107459703,859677624,6943550040,56540336040, 463630755528,3824953733106,31724616256938, 264371802141150,2212374554760150, 18583946259985260,156636118477018620] |