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) |
|---|---|
| 4 | 1 |
| 5 | 15 |
| 6 | 210 |
| 7 | 3150 |
| 8 | 51975 |
| 9 | 945945 |
| 10 | 18918900 |
| 11 | 413513100 |
| 12 | 9820936125 |
| 13 | 252070693875 |
| 14 | 6957151150950 |
| 15 | 205552193096250 |
| 16 | 6474894082531875 |
| 17 | 216659917377028125 |
| 18 | 7675951358500425000 |
| 19 | 287080580807915895000 |
| 20 | 11303797869311688365625 |
| 21 | 467445288360359818884375 |