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 | 17 |
| 3 | -47 |
| 4 | 545 |
| 5 | -3167 |
| 6 | 24113 |
| 7 | -162959 |
| 8 | 1158209 |
| 9 | -8054975 |
| 10 | 56542289 |
| 11 | -395323631 |
| 12 | 2768682593 |
| 13 | -19376526623 |
| 14 | 135648440945 |
| 15 | -949500822863 |
| 16 | 6646620551297 |
| 17 | -46525999485311 |
| 18 | 325683029518481 |
| 19 | -2279778107265455 |
| 20 | 15958456048949921 |
| 21 | -111709164448374239 |