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 | 4 |
| 1 | 49 |
| 2 | 499 |
| 3 | 4999 |
| 4 | 49999 |
| 5 | 499999 |
| 6 | 4999999 |
| 7 | 49999999 |
| 8 | 499999999 |
| 9 | 4999999999 |
| 10 | 49999999999 |
| 11 | 499999999999 |
| 12 | 4999999999999 |
| 13 | 49999999999999 |
| 14 | 499999999999999 |
| 15 | 4999999999999999 |
| 16 | 49999999999999999 |
| 17 | 499999999999999999 |
| 18 | 4999999999999999999 |
| 19 | 49999999999999999999 |
| 20 | 499999999999999999999 |