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 | 0 |
| 2 | 2 |
| 3 | -6 |
| 4 | 24 |
| 5 | -140 |
| 6 | 870 |
| 7 | -5922 |
| 8 | 45416 |
| 9 | -381096 |
| 10 | 3442410 |
| 11 | -33382910 |
| 12 | 345803172 |
| 13 | -3801763836 |
| 14 | 44156760830 |
| 15 | -539962736250 |
| 16 | 6929042527920 |
| 17 | -93032248209872 |
| 18 | 1303556965679826 |
| 19 | -19018807375195638 |
| 20 | 288341417011487420 |
| 21 | -4534168069704168420 |