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 | 8191 |
| 2 | 129442951 |
| 3 | 1820140085705 |
| 4 | 22606389934281147 |