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) |
|---|---|
| 0 | 0 |
| 1 | 81 |
| 2 | 891 |
| 3 | 8991 |
| 4 | 89991 |
| 5 | 899991 |
| 6 | 8999991 |
| 7 | 89999991 |
| 8 | 899999991 |
| 9 | 8999999991 |
| 10 | 89999999991 |
| 11 | 899999999991 |
| 12 | 8999999999991 |
| 13 | 89999999999991 |
| 14 | 899999999999991 |
| 15 | 8999999999999991 |
| 16 | 89999999999999991 |
| 17 | 899999999999999991 |
| 18 | 8999999999999999991 |
| 19 | 89999999999999999991 |
| 20 | 899999999999999999991 |