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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 135 |
| 6 | 1485 |
| 7 | 22275 |
| 8 | 378675 |
| 9 | 7952175 |
| 10 | 214708725 |
| 11 | 6226553025 |
| 12 | 217929355875 |
| 13 | 8499244879125 |
| 14 | 348469040044125 |
| 15 | 15681106801985625 |
| 16 | 799736446901266875 |
| 17 | 45584977473372211875 |
| 18 | 2689513670928960500625 |