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 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 4800 |
| 8 | 34752 |
| 9 | 280512 |
| 10 | 2528256 |
| 11 | 25282560 |
| 12 | 278323200 |
| 13 | 3289036800 |
| 14 | 42336448512 |
| 15 | 589351062528 |
| 16 | 8820501301248 |
| 17 | 141215147788800 |
| 18 | 2407845089203200 |
| 19 | 43543159894318080 |
| 20 | 832618225074748416 |
| 21 | 16782891792284791296 |