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 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 20 |
| 5 | 156 |
| 6 | 1472 |
| 7 | 17396 |
| 8 | 239612 |
| 9 | 3827816 |
| 10 | 69071272 |
| 11 | 1394315088 |
| 12 | 31081310944 |
| 13 | 758901184432 |
| 14 | 20135117147056 |
| 15 | 576927779925568 |
| 16 | 17752780676186432 |
| 17 | 583910574851160000 |
| 18 | 20443098012485430272 |
| 19 | 759064322969950283072 |
| 20 | 29793617955495321025472 |