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 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | 40 |
| 6 | 900 |
| 7 | 6048 |
| 8 | 43680 |
| 9 | 717120 |
| 10 | 8658720 |
| 11 | 102231360 |
| 12 | 1735525440 |
| 13 | 28819964160 |
| 14 | 473955850368 |
| 15 | 9235543363200 |
| 16 | 189202617676800 |
| 17 | 3940225003653120 |
| 18 | 89804740509434880 |
| 19 | 2169337606086389760 |
| 20 | 54085753764912844800 |
| 21 | 1429100881569205125120 |