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 | 13 |
| 2 | 135791113151719 |
| 3 | 135791113151719212325272931 |
| 4 | 135791113151719212325272931333537394143454749515355575961636567 |