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 | -2 |
| 5 | 6 |
| 6 | -18 |
| 7 | 57 |
| 8 | -186 |
| 9 | 622 |
| 10 | -2120 |
| 11 | 7338 |
| 12 | -25724 |
| 13 | 91144 |
| 14 | -325878 |
| 15 | 1174281 |
| 16 | -4260282 |
| 17 | 15548694 |
| 18 | -57048048 |
| 19 | 210295326 |
| 20 | -778483932 |
| 21 | 2892818244 |
| 22 | -10786724388 |
| 23 | 40347919626 |
| 24 | -151355847012 |
| 25 | 569274150156 |