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 | 5 |
| 4 | -12 |
| 5 | 69 |
| 6 | -285 |
| 7 | 2001 |
| 8 | -12208 |
| 9 | 104073 |
| 10 | -854865 |
| 11 | 8723549 |
| 12 | -90552396 |
| 13 | 1088372557 |
| 14 | -13647385661 |
| 15 | 190057979177 |
| 16 | -2787246189120 |
| 17 | 44285819490065 |
| 18 | -742019231348865 |
| 19 | 13267464006201781 |
| 20 | -249642268776311020 |