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 | -6 |
| 3 | 6 |
| 4 | 248 |
| 5 | -2120 |
| 6 | -12144 |
| 7 | 458416 |
| 8 | -2194560 |
| 9 | -102238848 |
| 10 | 2116494080 |
| 11 | 12999644416 |
| 12 | -1291721856000 |
| 13 | 14270887521280 |
| 14 | 650218659514368 |
| 15 | -24515781088389120 |
| 16 | -89087389799317504 |
| 17 | 27917287109308284928 |
| 18 | -556978307357438705664 |
| 19 | -23150337968775391281152 |