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 | 0 |
| 2 | 1 |
| 3 | 31 |
| 4 | 999 |
| 5 | 1000 |
| 6 | 31622 |
| 7 | 999999 |
| 8 | 1000000 |
| 9 | 31622776 |
| 10 | 999999999 |
| 11 | 1000000000 |
| 12 | 31622776601 |
| 13 | 999999999999 |
| 14 | 1000000000000 |
| 15 | 31622776601683 |
| 16 | 999999999999999 |
| 17 | 1000000000000000 |
| 18 | 31622776601683792 |
| 19 | 31622776601683793 |
| 20 | 999999999999999999 |
| 21 | 1000000000000000000 |