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 | -28 |
| 4 | 54 |
| 5 | 860 |
| 6 | -2004 |
| 7 | -33720 |
| 8 | 86054 |
| 9 | 1492908 |
| 10 | -4019452 |
| 11 | -71101832 |
| 12 | 198310460 |
| 13 | 3555617432 |
| 14 | -10168382696 |
| 15 | -184127171952 |
| 16 | 536496907782 |
| 17 | 9788598556876 |
| 18 | -28937139277804 |
| 19 | -531135371147368 |
| 20 | 1588378827366868 |
| 21 | 29295861148032584 |