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) |
|---|---|
| 1 | 49 |
| 2 | 409 |
| 3 | 4009 |
| 4 | 40009 |
| 5 | 400009 |
| 6 | 4000009 |
| 7 | 40000009 |
| 8 | 400000009 |
| 9 | 4000000009 |
| 10 | 40000000009 |
| 11 | 400000000009 |
| 12 | 4000000000009 |
| 13 | 40000000000009 |
| 14 | 400000000000009 |
| 15 | 4000000000000009 |
| 16 | 40000000000000009 |
| 17 | 400000000000000009 |
| 18 | 4000000000000000009 |
| 19 | 40000000000000000009 |
| 20 | 400000000000000000009 |
| 21 | 4000000000000000000009 |