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 | -4 |
| 3 | 24 |
| 4 | -96 |
| 5 | 0 |
| 6 | 5760 |
| 7 | -80640 |
| 8 | 645120 |
| 9 | 0 |
| 10 | -116121600 |
| 11 | 2554675200 |
| 12 | -30656102400 |
| 13 | 0 |
| 14 | 11158821273600 |
| 15 | -334764638208000 |
| 16 | 5356234211328000 |
| 17 | 0 |
| 18 | -3278015337332736000 |
| 19 | 124564582818643968000 |
| 20 | -2491291656372879360000 |
| 21 | 0 |