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 | 11 |
| 2 | 31 |
| 3 | 71 |
| 4 | 331 |
| 5 | 991 |
| 6 | 3331 |
| 7 | 33331 |
| 8 | 99991 |
| 9 | 333331 |
| 10 | 3333331 |
| 11 | 9999991 |
| 12 | 33333331 |
| 13 | 555555555551 |
| 14 | 5555555555551 |
| 15 | 7777777777771 |
| 16 | 333333333333333331 |
| 17 | 1111111111111111111 |
| 18 | 77777777777777777771 |
| 19 | 11111111111111111111111 |