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 | 3 |
| 3 | 3 |
| 4 | 15 |
| 5 | 33 |
| 6 | 105 |
| 7 | 297 |
| 8 | 879 |
| 9 | 2631 |
| 10 | 7833 |
| 11 | 23697 |
| 12 | 71385 |
| 13 | 216765 |
| 14 | 657849 |
| 15 | 2003151 |
| 16 | 6103743 |
| 17 | 18624693 |
| 18 | 56870385 |
| 19 | 173760513 |
| 20 | 531128349 |
| 21 | 1623881889 |
| 22 | 4965695331 |
| 23 | 15185222199 |
| 24 | 46435889601 |
| 25 | 141985777503 |