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 | 3 |
| 1 | 39 |
| 2 | 399 |
| 3 | 3999 |
| 4 | 39999 |
| 5 | 399999 |
| 6 | 3999999 |
| 7 | 39999999 |
| 8 | 399999999 |
| 9 | 3999999999 |
| 10 | 39999999999 |
| 11 | 399999999999 |
| 12 | 3999999999999 |
| 13 | 39999999999999 |
| 14 | 399999999999999 |
| 15 | 3999999999999999 |
| 16 | 39999999999999999 |
| 17 | 399999999999999999 |
| 18 | 3999999999999999999 |
| 19 | 39999999999999999999 |
| 20 | 399999999999999999999 |