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 | 1 |
| 1 | 9 |
| 2 | 99 |
| 3 | 990 |
| 4 | 9990 |
| 5 | 99891 |
| 6 | 999900 |
| 7 | 9998901 |
| 8 | 99998910 |
| 9 | 999989010 |
| 10 | 9999989010 |
| 11 | 99999889110 |
| 12 | 999999890109 |
| 13 | 9999998890200 |
| 14 | 99999998891100 |
| 15 | 999999988901199 |
| 16 | 9999999988902090 |
| 17 | 99999999888912090 |
| 18 | 999999999889011990 |
| 19 | 9999999998889021990 |