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 | -14 |
| 7 | 20 |
| 8 | 204 |
| 9 | 28 |
| 10 | -2584 |
| 11 | -6876 |
| 12 | 33760 |
| 13 | 219296 |
| 14 | -121848 |
| 15 | -6020456 |
| 16 | -15177904 |
| 17 | 126126960 |
| 18 | 950679424 |
| 19 | -898745392 |
| 20 | -38731873824 |
| 21 | -123922308896 |
| 22 | 1126028191520 |
| 23 | 10547325457536 |
| 24 | -5093629711808 |