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) |
|---|---|
| 1 | 6 |
| 2 | 20 |
| 3 | 42 |
| 4 | 1144 |
| 5 | 3343050 |
| 6 | 707866293437614080 |
| 7 | 322686644032484531917367528014184448000000 |