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 | 3 |
| 2 | 3 |
| 3 | 9 |
| 4 | 39 |
| 5 | 189 |
| 6 | 981 |
| 7 | 5490 |
| 8 | 31674 |
| 9 | 189954 |
| 10 | 1170126 |
| 11 | 7382745 |
| 12 | 47494197 |
| 13 | 310712808 |
| 14 | 2061987642 |
| 15 | 13855192866 |
| 16 | 94113385437 |
| 17 | 645424668666 |
| 18 | 4464027720900 |
| 19 | 31110200069511 |
| 20 | 218292811705458 |
| 21 | 1541172223659249 |