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 | 5 |
| 2 | -15 |
| 3 | 45 |
| 4 | -135 |
| 5 | 405 |
| 6 | -1215 |
| 7 | 3645 |
| 8 | -10935 |
| 9 | 32805 |
| 10 | -98415 |
| 11 | 295245 |
| 12 | -885735 |
| 13 | 2657205 |
| 14 | -7971615 |
| 15 | 23914845 |
| 16 | -71744535 |
| 17 | 215233605 |
| 18 | -645700815 |
| 19 | 1937102445 |
| 20 | -5811307335 |
| 21 | 17433922005 |
| 22 | -52301766015 |
| 23 | 156905298045 |
| 24 | -470715894135 |
| 25 | 1412147682405 |
| 26 | -4236443047215 |