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 | 5 |
| 2 | -20 |
| 3 | -145 |
| 4 | 355 |
| 5 | 3980 |
| 6 | -4895 |
| 7 | -104395 |
| 8 | 17980 |
| 9 | 2627855 |
| 10 | 2178355 |
| 11 | -63518020 |
| 12 | -117976895 |
| 13 | 1469973605 |
| 14 | 4419395980 |
| 15 | -32329944145 |
| 16 | -142814843645 |
| 17 | 665433759980 |
| 18 | 4235804851105 |
| 19 | -12400039148395 |
| 20 | -118295160426020 |
| 21 | 191705818283855 |