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 | -4 |
| 3 | 30 |
| 4 | -336 |
| 5 | 5040 |
| 6 | -95040 |
| 7 | 2162160 |
| 8 | -57657600 |
| 9 | 1764322560 |
| 10 | -60949324800 |
| 11 | 2346549004800 |
| 12 | -99638080819200 |
| 13 | 4626053752320000 |
| 14 | -233153109116928000 |
| 15 | 12677700308232960000 |
| 16 | -739781100339240960000 |
| 17 | 46113021921146019840000 |
| 18 | -3058021453718104473600000 |