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 | 0 |
| 3 | 1 |
| 4 | -5 |
| 5 | 23 |
| 6 | -129 |
| 7 | 894 |
| 8 | -7202 |
| 9 | 65365 |
| 10 | -661763 |
| 11 | 7412348 |
| 12 | -91009060 |
| 13 | 1214988851 |
| 14 | -17522921545 |
| 15 | 271538506004 |
| 16 | -4499710415184 |
| 17 | 79404970485241 |
| 18 | -1486680068450391 |
| 19 | 29435486083635796 |
| 20 | -614519419914446388 |