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 | 2 |
| 2 | 6 |
| 3 | 140 |
| 4 | 1287 |
| 5 | 2139552000 |
| 6 | 2949442889323392 |
| 7 | 322686644032484531917367528014184448000000 |