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 | -2 |
| 2 | -4 |
| 3 | 40 |
| 4 | 80 |
| 5 | -1952 |
| 6 | -3904 |
| 7 | 177280 |
| 8 | 354560 |
| 9 | -25866752 |
| 10 | -51733504 |
| 11 | 5535262720 |
| 12 | 11070525440 |
| 13 | -1633165156352 |
| 14 | -3266330312704 |
| 15 | 635421069967360 |
| 16 | 1270842139934720 |
| 17 | -315212388819402752 |
| 18 | -630424777638805504 |
| 19 | 194181169538675507200 |