The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 15 |
| 2 | 135 |
| 3 | 945 |
| 4 | 5670 |
| 5 | 30618 |
| 6 | 153090 |
| 7 | 721710 |
| 8 | 3247695 |
| 9 | 14073345 |
| 10 | 59108049 |
| 11 | 241805655 |
| 12 | 967222620 |
| 13 | 3794488740 |
| 14 | 14635885140 |
| 15 | 55616363532 |
| 16 | 208561363245 |
| 17 | 772903875555 |
| 18 | 2833980877035 |
| 19 | 10291825290285 |
| 20 | 37050571045026 |
[1,15,135,945,5670,30618,153090,721710,3247695, 14073345,59108049,241805655,967222620,3794488740, 14635885140,55616363532,208561363245,772903875555, 2833980877035,10291825290285,37050571045026] |