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 | 9 |
| 3 | 109 |
| 4 | 901 |
| 5 | 1009 |
| 6 | 9001 |
| 7 | 10009 |
| 8 | 10401 |
| 9 | 90001 |
| 10 | 100009 |
| 11 | 100901 |
| 12 | 900001 |
| 13 | 1000009 |
| 14 | 1004001 |
| 15 | 8954391 |
| 16 | 9000001 |
| 17 | 10000009 |
| 18 | 10009001 |
| 19 | 34351141 |
| 20 | 90000001 |
| 21 | 100000009 |
| 22 | 100040001 |
| 23 | 900000001 |
| 24 | 1000000009 |
| 25 | 1000090001 |
| 26 | 3163554991 |
| 27 | 9000000001 |
| 28 | 10000000009 |
| 29 | 10000400001 |