The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 12 |
| 3 | 552 |
| 4 | 6978816 |
| 5 | 429714433137180672 |
| 6 | 868161947968780041877535786874146453722578812928 |
[3,12,552,6978816,429714433137180672, 868161947968780041877535786874146453722578812928] |