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) |
|---|---|
| 1 | 1 |
| 2 | -2 |
| 3 | 4 |
| 4 | -18 |
| 5 | 6 |
| 6 | 1638 |
| 7 | -592 |
| 8 | 446088 |
| 9 | 39036424 |
| 10 | -284293536 |
| 11 | -1842401824 |
| 12 | 248900267136 |
| 13 | -15845288960 |
| 14 | -7495661063424 |
| 15 | 759742256093184 |
| 16 | -10356544812377088 |
| 17 | -3243279301721283584 |
| 18 | 12699358712830242816 |
| 19 | 4118558014200840683520 |
| 20 | -64593095335200293474304 |
| 21 | -1944280313362776777097216 |