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 | 2 |
| 3 | 6 |
| 4 | 3 |
| 5 | 15 |
| 6 | 720 |
| 7 | 5040 |
| 8 | 5040 |
| 9 | 45360 |
| 10 | 3628800 |
| 11 | 39916800 |
| 12 | 17740800 |
| 13 | 230630400 |
| 14 | 403603200 |
| 15 | 1307674368 |
| 16 | 20922789888 |
| 17 | 355687428096 |
| 18 | 51218989645824 |
| 19 | 973160803270656 |
| 20 | 2432902008176640000 |
| 21 | 5516784599040000 |