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 | 1 |
| 3 | -1 |
| 4 | 5 |
| 5 | 49 |
| 6 | 449 |
| 7 | 6131 |
| 8 | 25129 |
| 9 | 257825 |
| 10 | 2797409 |
| 11 | 97602559 |
| 12 | 1520338841 |
| 13 | 25975583789 |
| 14 | 245725626145 |
| 15 | 959689963259 |
| 16 | 22900048571009 |
| 17 | 1865034074530801 |
| 18 | 48689863762892609 |
| 19 | 1021947714097845815 |