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 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 272 |
| 7 | 1904 |
| 8 | 15232 |
| 9 | 124800 |
| 10 | 848640 |
| 11 | 7507200 |
| 12 | 39738368 |
| 13 | 433441792 |
| 14 | 2589116416 |
| 15 | 30419859456 |
| 16 | 486717751296 |
| 17 | 8128101580800 |
| 18 | 132557598294016 |
| 19 | 1971862458400768 |
| 20 | 30421253686034432 |
| 21 | 512675443057623040 |
| 22 | 7176891455747129344 |
| 23 | 130521457800367308800 |