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 | 1 |
| 4 | 8 |
| 5 | 15 |
| 6 | 720 |
| 7 | 5040 |
| 8 | 13440 |
| 9 | 13440 |
| 10 | 3628800 |
| 11 | 532224 |
| 12 | 43545600 |
| 13 | 691891200 |
| 14 | 691891200 |
| 15 | 108972864000 |
| 16 | 1902071808000 |
| 17 | 118562476032000 |
| 18 | 6847458508800 |
| 19 | 24329020081766400 |
| 20 | 17888985354240000 |
| 21 | 1344498478202880000 |