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 | 4 |
| 5 | 6 |
| 6 | 60 |
| 7 | 120 |
| 8 | 1920 |
| 9 | 7560 |
| 10 | 90720 |
| 11 | 362880 |
| 12 | 13305600 |
| 13 | 39916800 |
| 14 | 1037836800 |
| 15 | 10897286400 |
| 16 | 265686220800 |
| 17 | 1307674368000 |
| 18 | 66691392768000 |
| 19 | 355687428096000 |
| 20 | 20274183401472000 |
| 21 | 202741834014720000 |