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 | 1 |
| 2 | -2 |
| 3 | 11 |
| 4 | -96 |
| 5 | 1080 |
| 6 | -13776 |
| 7 | 179592 |
| 8 | -2257536 |
| 9 | 36167616 |
| 10 | -1328400000 |
| 11 | 53474351040 |
| 12 | -364978483200 |
| 13 | -111366266618880 |
| 14 | 2057176091013120 |
| 15 | 861071536310630400 |
| 16 | -50092279632602726400 |
| 17 | -9303569614922165452800 |
| 18 | 1142810852264472571084800 |
| 19 | 154051064897857365779251200 |
| 20 | -35956459453770594679062528000 |