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 | 2 |
| 3 | -3 |
| 4 | 18 |
| 5 | -150 |
| 6 | 1518 |
| 7 | -17541 |
| 8 | 223782 |
| 9 | -3087948 |
| 10 | 45470022 |
| 11 | -707810715 |
| 12 | 11569008816 |
| 13 | -197540043324 |
| 14 | 3509923686678 |
| 15 | -64697804055675 |
| 16 | 1234127209128306 |
| 17 | -24312707152663590 |
| 18 | 493834352052852738 |
| 19 | -10327320248199824889 |
| 20 | 222086739445484152590 |