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 | 2 |
| 4 | 8 |
| 5 | 64 |
| 6 | 640 |
| 7 | 8960 |
| 8 | 143360 |
| 9 | 2867200 |
| 10 | 74547200 |
| 11 | 2087321600 |
| 12 | 70968934400 |
| 13 | 2696819507200 |
| 14 | 107872780288000 |
| 15 | 4746402332672000 |
| 16 | 237320116633600000 |
| 17 | 13289926531481600000 |
| 18 | 770815738825932800000 |
| 19 | 49332207284859699200000 |
| 20 | 3354590095370459545600000 |
| 21 | 234821306675932168192000000 |