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 | 0 |
| 2 | 0 |
| 3 | 3 |
| 4 | 18 |
| 5 | 100 |
| 6 | 615 |
| 7 | 4326 |
| 8 | 34636 |
| 9 | 311760 |
| 10 | 3117645 |
| 11 | 34294150 |
| 12 | 411529866 |
| 13 | 5349888336 |
| 14 | 74898436795 |
| 15 | 1123476552030 |
| 16 | 17975624832600 |
| 17 | 305585622154336 |
| 18 | 5500541198778201 |
| 19 | 104510282776785990 |
| 20 | 2090205655535719990 |
| 21 | 43894318766250120000 |