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 | 20 |
| 6 | 315 |
| 7 | 4620 |
| 8 | 67830 |
| 9 | 1020600 |
| 10 | 15961050 |
| 11 | 260706600 |
| 12 | 4461170175 |
| 13 | 80002622700 |
| 14 | 1503527550525 |
| 15 | 29583578524500 |
| 16 | 608837350621500 |
| 17 | 13088359506222000 |
| 18 | 293538127312930500 |
| 19 | 6858722586405690000 |
| 20 | 166752692881988338125 |