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 | 3 |
| 2 | 15 |
| 3 | 72 |
| 4 | 361 |
| 5 | 1840 |
| 6 | 9505 |
| 7 | 49578 |
| 8 | 260540 |
| 9 | 1377328 |
| 10 | 7316373 |
| 11 | 39020372 |
| 12 | 208809544 |
| 13 | 1120621368 |
| 14 | 6029023185 |
| 15 | 32507001876 |
| 16 | 175604614108 |
| 17 | 950233307930 |
| 18 | 5149691511432 |
| 19 | 27946158749572 |
| 20 | 151843410356906 |
| 21 | 825949622559366 |