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 | 2 |
| 2 | -2 |
| 3 | 6 |
| 4 | -22 |
| 5 | 90 |
| 6 | -394 |
| 7 | 1806 |
| 8 | -8558 |
| 9 | 41586 |
| 10 | -206098 |
| 11 | 1037718 |
| 12 | -5293446 |
| 13 | 27297738 |
| 14 | -142078746 |
| 15 | 745387038 |
| 16 | -3937603038 |
| 17 | 20927156706 |
| 18 | -111818026018 |
| 19 | 600318853926 |
| 20 | -3236724317174 |
| 21 | 17518619320890 |
| 22 | -95149655201962 |
| 23 | 518431875418926 |
| 24 | -2832923350929742 |
| 25 | 15521467648875090 |