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 | 2 |
| 3 | 12 |
| 4 | 50 |
| 5 | 280 |
| 6 | 1442 |
| 7 | 7812 |
| 8 | 42338 |
| 9 | 232176 |
| 10 | 1280642 |
| 11 | 7103932 |
| 12 | 39579410 |
| 13 | 221340808 |
| 14 | 1241708834 |
| 15 | 6984796852 |
| 16 | 39382895810 |
| 17 | 222512915680 |
| 18 | 1259482604546 |
| 19 | 7140546372204 |
| 20 | 40541480041970 |
| 21 | 230480474747640 |
| 22 | 1311841695315362 |
| 23 | 7474722997813732 |
| 24 | 42631911134818850 |