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 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 0 |
| 5 | -4 |
| 6 | 0 |
| 7 | 120 |
| 8 | 0 |
| 9 | -12096 |
| 10 | 0 |
| 11 | 3024000 |
| 12 | 0 |
| 13 | -1576143360 |
| 14 | 0 |
| 15 | 1525620096000 |
| 16 | 0 |
| 17 | -2522591034163200 |
| 18 | 0 |
| 19 | 6686974460694528000 |
| 20 | 0 |
| 21 | -27033456071346536448000 |
| 22 | 0 |
| 23 | 160078872315904478576640000 |
| 24 | 0 |
| 25 | -1342964491649083924630732800000 |
| 26 | 0 |
| 27 | 15522270327163593186886877184000000 |
| 28 | 0 |