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 | -2 |
| 4 | 7 |
| 5 | 51 |
| 6 | -239 |
| 7 | -2435 |
| 8 | 16353 |
| 9 | 209377 |
| 10 | -1826099 |
| 11 | -28232379 |
| 12 | 303020125 |
| 13 | 5494172893 |
| 14 | -70032035163 |
| 15 | -1457369472299 |
| 16 | 21512472563281 |
| 17 | 505400696581905 |
| 18 | -8478758871011807 |
| 19 | -221971772323923263 |
| 20 | 4171251104170567101 |
| 21 | 120416449897739144941 |