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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 6 |
| 4 | -27 |
| 5 | 164 |
| 6 | -1133 |
| 7 | 8930 |
| 8 | -78739 |
| 9 | 768276 |
| 10 | -8221025 |
| 11 | 95775678 |
| 12 | -1207356591 |
| 13 | 16381797128 |
| 14 | -238127430413 |
| 15 | 3693030808322 |
| 16 | -60880099651291 |
| 17 | 1063264668030924 |
| 18 | -19614400226382041 |
| 19 | 381146295159812646 |
| 20 | -7782393142569110535 |
| 21 | 166592263396576831760 |