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 | 0 |
| 2 | 1 |
| 3 | -1 |
| 4 | 5 |
| 5 | -11 |
| 6 | 43 |
| 7 | -127 |
| 8 | 489 |
| 9 | -1693 |
| 10 | 6771 |
| 11 | -26071 |
| 12 | 109693 |
| 13 | -457757 |
| 14 | 2028671 |
| 15 | -9039931 |
| 16 | 42101329 |
| 17 | -198411489 |
| 18 | 967906675 |
| 19 | -4791497559 |
| 20 | 24401815141 |
| 21 | -126243354637 |
| 22 | 669094876055 |
| 23 | -3603105436163 |
| 24 | 19818039219577 |
| 25 | -110721426757801 |
| 26 | 630419303537115 |