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 | 2 |
| 4 | -3 |
| 5 | 12 |
| 6 | -35 |
| 7 | 121 |
| 8 | -413 |
| 9 | 1464 |
| 10 | -5265 |
| 11 | 19249 |
| 12 | -71236 |
| 13 | 266443 |
| 14 | -1005511 |
| 15 | 3824055 |
| 16 | -14641264 |
| 17 | 56389272 |
| 18 | -218315173 |
| 19 | 849170605 |
| 20 | -3316817080 |
| 21 | 13004273475 |
| 22 | -51160638706 |
| 23 | 201901154910 |
| 24 | -799059730844 |
| 25 | 3170706566751 |
| 26 | -12611882813645 |
| 27 | 50277271079611 |