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 | -1 |
| 4 | 19 |
| 5 | -5 |
| 6 | 253 |
| 7 | -61 |
| 8 | 3319 |
| 9 | -1385 |
| 10 | 222557 |
| 11 | -50521 |
| 12 | 422152729 |
| 13 | -2702765 |
| 14 | 59833795 |
| 15 | -199360981 |
| 16 | 439264083023 |
| 17 | -19391512145 |
| 18 | 76632373664299 |
| 19 | -2404879675441 |
| 20 | 4432283799315809 |
| 21 | -370371188237525 |