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 | 1 |
| 5 | -1 |
| 6 | 1 |
| 7 | -1 |
| 8 | 3 |
| 9 | -15 |
| 10 | 59 |
| 11 | -189 |
| 12 | 567 |
| 13 | -1863 |
| 14 | 7141 |
| 15 | -29817 |
| 16 | 125919 |
| 17 | -528329 |
| 18 | 2238303 |
| 19 | -9769917 |
| 20 | 44312225 |
| 21 | -208177669 |
| 22 | 1005840685 |
| 23 | -4972561375 |
| 24 | 25105651267 |
| 25 | -129470605611 |
| 26 | 682486916465 |
| 27 | -3678964401327 |
| 28 | 20276967904907 |
| 29 | -114199064797229 |
| 30 | 656666370592173 |