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 | 0 |
| 2 | -1 |
| 3 | 3 |
| 4 | -9 |
| 5 | 30 |
| 6 | -109 |
| 7 | 420 |
| 8 | -1685 |
| 9 | 6960 |
| 10 | -29391 |
| 11 | 126291 |
| 12 | -550359 |
| 13 | 2426502 |
| 14 | -10803801 |
| 15 | 48507843 |
| 16 | -219377949 |
| 17 | 998436792 |
| 18 | -4569488371 |
| 19 | 21016589073 |
| 20 | -97090411019 |
| 21 | 450314942682 |
| 22 | -2096122733211 |
| 23 | 9788916220518 |