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 | 31 |
| 2 | 301 |
| 3 | 3001 |
| 4 | 30001 |
| 5 | 300001 |
| 6 | 3000001 |
| 7 | 30000001 |
| 8 | 300000001 |
| 9 | 3000000001 |
| 10 | 30000000001 |
| 11 | 300000000001 |
| 12 | 3000000000001 |
| 13 | 30000000000001 |
| 14 | 300000000000001 |
| 15 | 3000000000000001 |
| 16 | 30000000000000001 |
| 17 | 300000000000000001 |
| 18 | 3000000000000000001 |
| 19 | 30000000000000000001 |
| 20 | 300000000000000000001 |