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 | 3 |
| 4 | 18 |
| 5 | 75 |
| 6 | 270 |
| 7 | 903 |
| 8 | 2898 |
| 9 | 9075 |
| 10 | 27990 |
| 11 | 85503 |
| 12 | 259578 |
| 13 | 784875 |
| 14 | 2366910 |
| 15 | 7125303 |
| 16 | 21425058 |
| 17 | 64373475 |
| 18 | 193317030 |
| 19 | 580344303 |
| 20 | 1741819338 |
| 21 | 5227030875 |
| 22 | 15684238350 |
| 23 | 47059006503 |
| 24 | 141189602418 |
| 25 | 423593973075 |
| 26 | 1270832250870 |