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 | 1 |
| 2 | 121 |
| 3 | 12321 |
| 4 | 1234321 |
| 5 | 123454321 |
| 6 | 12345654321 |
| 7 | 1234567654321 |
| 8 | 123456787654321 |
| 9 | 12345678987654321 |
| 10 | 1234567900987654321 |
| 11 | 123456790120987654321 |
| 12 | 12345679012320987654321 |
| 13 | 1234567901234320987654321 |