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 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 72 |
| 5 | 340 |
| 6 | 1688 |
| 7 | 8648 |
| 8 | 45468 |
| 9 | 243832 |
| 10 | 1328800 |
| 11 | 7337500 |
| 12 | 40965984 |
| 13 | 230864496 |
| 14 | 1311526532 |
| 15 | 7502799104 |
| 16 | 43183861352 |
| 17 | 249897858164 |
| 18 | 1453076715976 |
| 19 | 8485587751112 |
| 20 | 49745923115916 |
| 21 | 292655237446616 |
| 22 | 1727193226708608 |