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 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 36 |
| 5 | 250 |
| 6 | 2100 |
| 7 | 20594 |
| 8 | 231168 |
| 9 | 2923722 |
| 10 | 41149140 |
| 11 | 637972522 |
| 12 | 10804678632 |
| 13 | 198480649250 |
| 14 | 3930963078588 |
| 15 | 83500876635570 |
| 16 | 1893745346613216 |
| 17 | 45672635292831322 |
| 18 | 1167233799092342148 |
| 19 | 31510575263852229242 |
| 20 | 896028017040096045720 |