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 | -19 |
| 4 | 73 |
| 5 | -401 |
| 6 | 5191 |
| 7 | -29779 |
| 8 | 879089 |
| 9 | -7232833 |
| 10 | 103048111 |
| 11 | -1891058291 |
| 12 | 31696845049 |
| 13 | -649348332049 |
| 14 | 9310670445623 |
| 15 | -270217657103731 |
| 16 | 5480877008565601 |
| 17 | -131578355696804609 |
| 18 | 3133521575795986399 |
| 19 | -81890613282163881043 |
| 20 | 2460096066325021029161 |