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) |
|---|---|
| 0 | 1 |
| 1 | -1 |
| 2 | 0 |
| 3 | 1 |
| 4 | -1 |
| 5 | -1 |
| 6 | 4 |
| 7 | -1 |
| 8 | -19 |
| 9 | 31 |
| 10 | 120 |
| 11 | -483 |
| 12 | -933 |
| 13 | 8623 |
| 14 | 6748 |
| 15 | -189589 |
| 16 | 41561 |
| 17 | 5147391 |
| 18 | -6328400 |
| 19 | -170622599 |
| 20 | 394612599 |
| 21 | 6807529823 |
| 22 | -23890335372 |
| 23 | -322371010985 |
| 24 | 1564733285829 |
| 25 | 17884889743135 |
| 26 | -114158790326872 |