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 | 21 |
| 4 | 136 |
| 5 | 1030 |
| 6 | 8856 |
| 7 | 84861 |
| 8 | 894928 |
| 9 | 10291986 |
| 10 | 128165720 |
| 11 | 1718395602 |
| 12 | 24686953968 |
| 13 | 378444958060 |
| 14 | 6167922926704 |
| 15 | 106525443913245 |
| 16 | 1943838547593888 |
| 17 | 37375737467294362 |
| 18 | 755393226726677976 |
| 19 | 16011417246585359046 |
| 20 | 355187993770520180400 |
| 21 | 8230524179585799932820 |