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) |
|---|---|
| 4 | 0 |
| 5 | -3 |
| 6 | 15 |
| 7 | -45 |
| 8 | 0 |
| 9 | 1260 |
| 10 | -11340 |
| 11 | 56700 |
| 12 | 0 |
| 13 | -3742200 |
| 14 | 48648600 |
| 15 | -340540200 |
| 16 | 0 |
| 17 | 40864824000 |
| 18 | -694702008000 |
| 19 | 6252318072000 |
| 20 | 0 |
| 21 | -1187940433680000 |
| 22 | 24946749107280000 |
| 23 | -274414240180080000 |
| 24 | 0 |
| 25 | 75738330289702080000 |
| 26 | -1893458257242552000000 |
| 27 | 24614957344153176000000 |
| 28 | 0 |