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 | 3 |
| 6 | -2 |
| 7 | 25 |
| 8 | -213 |
| 9 | 1547 |
| 10 | -13276 |
| 11 | 129069 |
| 12 | -1375775 |
| 13 | 16009741 |
| 14 | -202184274 |
| 15 | 2753591087 |
| 16 | -40231298023 |
| 17 | 627731583225 |
| 18 | -10418193719432 |
| 19 | 183264681827863 |
| 20 | -3406106373633009 |
| 21 | 66695477905719251 |
| 22 | -1372395141298236250 |
| 23 | 29607108539572186329 |