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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 24 |
| 5 | 60 |
| 6 | 240 |
| 7 | 1260 |
| 8 | -12096 |
| 9 | -120960 |
| 10 | -1144800 |
| 11 | -11642400 |
| 12 | 190270080 |
| 13 | 4670265600 |
| 14 | 81378198720 |
| 15 | 1348668921600 |
| 16 | -880532674560 |
| 17 | -406217626214400 |
| 18 | -13255586359142400 |
| 19 | -343166884178227200 |
| 20 | -3137937973466572800 |
| 21 | 72862796986940620800 |