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) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 6 |
| 6 | 6 |
| 7 | 0 |
| 8 | 18 |
| 9 | 54 |
| 10 | 0 |
| 11 | 258 |
| 12 | 612 |
| 13 | 0 |
| 14 | 3570 |
| 15 | 8880 |
| 16 | 0 |
| 17 | 55764 |
| 18 | 142368 |
| 19 | 0 |
| 20 | 947946 |
| 21 | 2468844 |
| 22 | 0 |
| 23 | 17099808 |
| 24 | 45375498 |
| 25 | 0 |
| 26 | 323927184 |
| 27 | 871038570 |
| 28 | 0 |
| 29 | 6369199908 |
| 30 | 17312303760 |