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 | 19 |
| 3 | -1 |
| 4 | 39 |
| 5 | 49999 |
| 6 | -1 |
| 7 | 69999 |
| 8 | 79 |
| 9 | -1 |
| 10 | 18999999999 |
| 11 | 2899999 |
| 12 | -1 |
| 13 | 48999 |
| 14 | 5899999999999 |
| 15 | -1 |
| 16 | 78999999999 |
| 17 | 8899 |
| 18 | -1 |
| 19 | 19899999999999999999 |
| 20 | 298999999999 |
| 21 | -1 |
| 22 | 49899999 |
| 23 | 598999999999999999999 |
| 24 | -1 |
| 25 | 79899999999999999 |
| 26 | 898999 |
| 27 | -1 |
| 28 | 19989999999999999999999999999 |
| 29 | 29989999999999999 |
| 30 | -1 |