The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 18 |
| 4 | 189 |
| 5 | 3000 |
| 6 | 84060 |
| 7 | 2799360 |
| 8 | 148771080 |
| 9 | 8457799680 |
| 10 | 727583990400 |
| 11 | 53828906153760 |
[1,3,18,189,3000,84060,2799360,148771080, 8457799680,727583990400,53828906153760] |