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 | 7 |
| 3 | -21 |
| 4 | 81 |
| 5 | -295 |
| 6 | 1107 |
| 7 | -4165 |
| 8 | 15793 |
| 9 | -60171 |
| 10 | 230253 |
| 11 | -884235 |
| 12 | 3406105 |
| 13 | -13154947 |
| 14 | 50922987 |
| 15 | -197519941 |
| 16 | 767502945 |
| 17 | -2987013067 |
| 18 | 11641557717 |
| 19 | -45429853651 |
| 20 | 177490745985 |
| 21 | -694175171647 |
| 22 | 2717578296117 |
| 23 | -10648297329691 |
| 24 | 41757352712481 |
| 25 | -163875286898935 |