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 | 19 |
| 2 | 109 |
| 3 | 991 |
| 4 | 1009 |
| 5 | 10009 |
| 6 | 99991 |
| 7 | 9999991 |
| 8 | 1000000009 |
| 9 | 1000000000000000009 |
| 10 | 10000000000000000000009 |
| 11 | 999999999999999999999999999999991 |
| 12 | 999999999999999999999999999999999999999999991 |
| 13 | 1000000000000000000000000000000000000000000009 |