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 | 7 |
| 3 | -36 |
| 4 | 246 |
| 5 | -2100 |
| 6 | 21510 |
| 7 | -257040 |
| 8 | 3510360 |
| 9 | -53933040 |
| 10 | 920694600 |
| 11 | -17288964000 |
| 12 | 354169292400 |
| 13 | -7859862410400 |
| 14 | 187846741882800 |
| 15 | -4810116703392000 |
| 16 | 131382125482608000 |
| 17 | -3812816394747360000 |
| 18 | 117159925012065936000 |
| 19 | -3800085546956707008000 |
| 20 | 129743036125975752480000 |