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 | 5 |
| 2 | 25 |
| 3 | 125 |
| 4 | 630 |
| 5 | 3206 |
| 6 | 16470 |
| 7 | 85350 |
| 8 | 445775 |
| 9 | 2344595 |
| 10 | 12408903 |
| 11 | 66042795 |
| 12 | 353259900 |
| 13 | 1898119100 |
| 14 | 10240583420 |
| 15 | 55454182716 |
| 16 | 301307002605 |
| 17 | 1642192132625 |
| 18 | 8975693643525 |
| 19 | 49186242980105 |
| 20 | 270186765784210 |