This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 24 |
| 4 | 280 |
| 5 | 3400 |
| 6 | 212538 |
| 7 | 2708944 |
| 8 | 244962336 |
| 9 | 3195918288 |
| 10 | 42013225014 |
| 11 | 111125508824 |
| 12 | 11603576403816 |
| 13 | 30966112647080 |
| 14 | 188641282541015866 |
| 15 | 2532986569522773024 |
| 16 | 34096877865475065728 |
| 17 | 459984329860282638816 |
| 18 | 105694712757690117569946 |
| 19 | 1431044069320995796765272 |
| 20 | 73738714208458783084303688 |