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 | 0 |
| 3 | -3 |
| 4 | 0 |
| 5 | 45 |
| 6 | 0 |
| 7 | -1575 |
| 8 | 0 |
| 9 | 99225 |
| 10 | 0 |
| 11 | -9823275 |
| 12 | 0 |
| 13 | 1404728325 |
| 14 | 0 |
| 15 | -273922023375 |
| 16 | 0 |
| 17 | 69850115960625 |
| 18 | 0 |
| 19 | -22561587455281875 |
| 20 | 0 |
| 21 | 9002073394657468125 |
| 22 | 0 |
| 23 | -4348001449619557104375 |
| 24 | 0 |
| 25 | 2500100833531245335015625 |
| 26 | 0 |
| 27 | -1687568062633590601135546875 |