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 | 9 |
| 2 | 63 |
| 3 | 345 |
| 4 | 1665 |
| 5 | 7227 |
| 6 | 29073 |
| 7 | 109791 |
| 8 | 394020 |
| 9 | 1354210 |
| 10 | 4486482 |
| 11 | 14397318 |
| 12 | 44932446 |
| 13 | 136817370 |
| 14 | 407566350 |
| 15 | 1190446866 |
| 16 | 3415935699 |
| 17 | 9645169743 |
| 18 | 26836557825 |
| 19 | 73670997015 |
| 20 | 199751003991 |
| 21 | 535449185469 |