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 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 135 |
| 6 | 1215 |
| 7 | 2835 |
| 8 | 127575 |
| 9 | 229635 |
| 10 | 3444525 |
| 11 | 1705039875 |
| 12 | 107417512125 |
| 13 | 13299311025 |
| 14 | 4189282972875 |
| 15 | 62839244593125 |
| 16 | 188517733779375 |
| 17 | 336504154796184375 |
| 18 | 9085612179496978125 |
| 19 | 2740105260483215625 |