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 | 2 |
| 5 | 6 |
| 6 | 25 |
| 7 | 88 |
| 8 | 335 |
| 9 | 1215 |
| 10 | 4534 |
| 11 | 16823 |
| 12 | 63159 |
| 13 | 237679 |
| 14 | 900341 |
| 15 | 3423201 |
| 16 | 13073163 |
| 17 | 50095285 |
| 18 | 192599091 |
| 19 | 742576616 |
| 20 | 2870584814 |
| 21 | 11122879867 |
| 22 | 43191525139 |
| 23 | 168046317330 |
| 24 | 654998425237 |
| 25 | 2557224396342 |
| 26 | 9999083912711 |
| 27 | 39153000738695 |
| 28 | 153511081627903 |