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 | 21 |
| 2 | 201 |
| 3 | 2001 |
| 4 | 20001 |
| 5 | 200001 |
| 6 | 2000001 |
| 7 | 20000001 |
| 8 | 200000001 |
| 9 | 2000000001 |
| 10 | 20000000001 |
| 11 | 200000000001 |
| 12 | 2000000000001 |
| 13 | 20000000000001 |
| 14 | 200000000000001 |
| 15 | 2000000000000001 |
| 16 | 20000000000000001 |
| 17 | 200000000000000001 |
| 18 | 2000000000000000001 |