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) |
|---|---|
| 2 | 1 |
| 3 | -552 |
| 4 | 8640 |
| 5 | 116000 |
| 6 | -4868460 |
| 7 | 67855536 |
| 8 | -544522240 |
| 9 | 2742137280 |
| 10 | -8237774250 |
| 11 | 10592091400 |
| 12 | 3366617856 |
| 13 | 113971542048 |
| 14 | -1217020425880 |
| 15 | 4535746506000 |
| 16 | -5415752171520 |
| 17 | -19090509870144 |
| 18 | 93580817811453 |
| 19 | -142801363479240 |
| 20 | -80721277168000 |
| 21 | 665065363025280 |