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 | 6 |
| 3 | 24 |
| 4 | 72 |
| 5 | 144 |
| 6 | 0 |
| 7 | -1728 |
| 8 | -10368 |
| 9 | -41472 |
| 10 | -124416 |
| 11 | -248832 |
| 12 | 0 |
| 13 | 2985984 |
| 14 | 17915904 |
| 15 | 71663616 |
| 16 | 214990848 |
| 17 | 429981696 |
| 18 | 0 |
| 19 | -5159780352 |
| 20 | -30958682112 |
| 21 | -123834728448 |
| 22 | -371504185344 |
| 23 | -743008370688 |
| 24 | 0 |
| 25 | 8916100448256 |
| 26 | 53496602689536 |
| 27 | 213986410758144 |
| 28 | 641959232274432 |