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 | -1 |
| 3 | -7 |
| 4 | 25 |
| 5 | -41 |
| 6 | 631 |
| 7 | 881 |
| 8 | 98897 |
| 9 | -609265 |
| 10 | 3798991 |
| 11 | -41799671 |
| 12 | 914146729 |
| 13 | -15008576857 |
| 14 | 16469525255 |
| 15 | -5181463756351 |
| 16 | 79515495724321 |
| 17 | -1220435382764129 |
| 18 | 12608713897126687 |
| 19 | -449855614172366695 |
| 20 | 10437031873016276921 |
| 21 | -231918657853281955081 |