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 | 41 |
| 2 | 491 |
| 3 | 4991 |
| 4 | 49991 |
| 5 | 499991 |
| 6 | 4999991 |
| 7 | 49999991 |
| 8 | 499999991 |
| 9 | 4999999991 |
| 10 | 49999999991 |
| 11 | 499999999991 |
| 12 | 4999999999991 |
| 13 | 49999999999991 |
| 14 | 499999999999991 |
| 15 | 4999999999999991 |
| 16 | 49999999999999991 |
| 17 | 499999999999999991 |
| 18 | 4999999999999999991 |
| 19 | 49999999999999999991 |
| 20 | 499999999999999999991 |