The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 20 |
| 3 | 234 |
| 4 | 3944 |
| 5 | 86400 |
| 6 | 2324160 |
| 7 | 74062800 |
| 8 | 2726970624 |
| 9 | 113893395840 |
| 10 | 5319595814400 |
| 11 | 274730601277440 |
| 12 | 15544557784673280 |
| 13 | 956232958853652480 |
| 14 | 63540675378122342400 |
| 15 | 4535620918350762240000 |
| 16 | 346127227962539155292160 |
| 17 | 28120835253815298895380480 |
| 18 | 2423309442415144546546483200 |
[1,3,20,234,3944,86400,2324160,74062800, 2726970624,113893395840,5319595814400, 274730601277440,15544557784673280, 956232958853652480,63540675378122342400, 4535620918350762240000,346127227962539155292160, 28120835253815298895380480, 2423309442415144546546483200] |