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 | 1 |
| 3 | 4 |
| 4 | 19 |
| 5 | 107 |
| 6 | 682 |
| 7 | 4915 |
| 8 | 39871 |
| 9 | 361138 |
| 10 | 3621531 |
| 11 | 39884367 |
| 12 | 478847750 |
| 13 | 6226248403 |
| 14 | 87174202427 |
| 15 | 1307651621142 |
| 16 | 20922657286067 |
| 17 | 355686620215179 |
| 18 | 6402368573492818 |
| 19 | 121645066483568099 |
| 20 | 2432901775271051559 |
| 21 | 51090940513901948778 |