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 | 4 |
| 2 | 20 |
| 3 | 104 |
| 4 | 552 |
| 5 | 2892 |
| 6 | 14908 |
| 7 | 75952 |
| 8 | 384080 |
| 9 | 1933460 |
| 10 | 9706596 |
| 11 | 48651000 |
| 12 | 243609208 |
| 13 | 1219108828 |
| 14 | 6098732684 |
| 15 | 30503229248 |
| 16 | 152544843936 |
| 17 | 762810312996 |
| 18 | 3814309845172 |
| 19 | 19072324066696 |
| 20 | 95363944856264 |
| 21 | 476826697849964 |