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 | 10 |
| 2 | 90 |
| 3 | 990 |
| 4 | 9900 |
| 5 | 99990 |
| 6 | 998910 |
| 7 | 9999990 |
| 8 | 99990000 |
| 9 | 999999000 |
| 10 | 9999899910 |
| 11 | 99999999990 |
| 12 | 999998990100 |
| 13 | 9999999999990 |
| 14 | 99999989999910 |
| 15 | 999999999899010 |
| 16 | 9999999900000000 |
| 17 | 99999999999999990 |
| 18 | 999999998999001000 |
| 19 | 9999999999999999990 |
| 20 | 99999999989999990100 |