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 | 990 |
| 2 | 809809890 |
| 3 | 89909089088809980 |
| 4 | 98899080989088808000999800 |