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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | -1 |
| 5 | 0 |
| 6 | -1 |
| 7 | -1 |
| 8 | 17 |
| 9 | 587 |
| 10 | 3151 |
| 11 | -173 |
| 12 | -2641109 |
| 13 | -6343201 |
| 14 | 29002301 |
| 15 | 24753572807 |
| 16 | 6013935944287 |
| 17 | -979056822493 |
| 18 | -11395219462649 |
| 19 | -4313800586682649 |
| 20 | -2178360615103441 |
| 21 | 74893762899375939059 |
| 22 | 5307412498351127900521 |