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 | 4 |
| 4 | 24 |
| 5 | 136 |
| 6 | 480 |
| 7 | 4768 |
| 8 | 40320 |
| 9 | 249856 |
| 10 | 4112640 |
| 11 | 39563008 |
| 12 | 319334400 |
| 13 | 6249389056 |
| 14 | 82473431040 |
| 15 | 1044235737088 |
| 16 | 20922789888000 |
| 17 | 355897293438976 |
| 18 | 4408265775513600 |
| 19 | 121616011523719168 |
| 20 | 2757288942600192000 |
| 21 | 31308290669925892096 |