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 | 90 |
| 2 | 9900 |
| 3 | 999000 |
| 4 | 99990000 |
| 5 | 9999900000 |
| 6 | 999999000000 |
| 7 | 99999990000000 |
| 8 | 9999999900000000 |
| 9 | 999999999000000000 |
| 10 | 99999999990000000000 |
| 11 | 9999999999900000000000 |
| 12 | 999999999999000000000000 |
| 13 | 99999999999990000000000000 |
| 14 | 9999999999999900000000000000 |
| 15 | 999999999999999000000000000000 |