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 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | -1 |
| 4 | 7 |
| 5 | -13 |
| 6 | 55 |
| 7 | -133 |
| 8 | 463 |
| 9 | -1261 |
| 10 | 4039 |
| 11 | -11605 |
| 12 | 35839 |
| 13 | -105469 |
| 14 | 320503 |
| 15 | -953317 |
| 16 | 2876335 |
| 17 | -8596237 |
| 18 | 25854247 |
| 19 | -77431669 |
| 20 | 232557151 |
| 21 | -697147165 |
| 22 | 2092490071 |
| 23 | -6275373061 |
| 24 | 18830313487 |
| 25 | -56482551853 |
| 26 | 169464432775 |
| 27 | -508359743893 |
| 28 | 1525146340543 |