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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 2 |
| 6 | 14 |
| 7 | 68 |
| 8 | 274 |
| 9 | 986 |
| 10 | 3288 |
| 11 | 10416 |
| 12 | 31872 |
| 13 | 95382 |
| 14 | 281762 |
| 15 | 827084 |
| 16 | 2423078 |
| 17 | 7102598 |
| 18 | 20852296 |
| 19 | 61323328 |
| 20 | 180581128 |
| 21 | 532199414 |
| 22 | 1569071842 |
| 23 | 4626551740 |
| 24 | 13641716894 |
| 25 | 40223795038 |
| 26 | 118614194080 |
| 27 | 349847093824 |
| 28 | 1032173428200 |