The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 25 |
| 4 | 408 |
| 5 | 18003 |
| 6 | 2289232 |
| 7 | 851979730 |
| 8 | 942937083934 |
| 9 | 3094296827345219 |
[2,4,25,408,18003,2289232,851979730,942937083934, 3094296827345219] |