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) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 72 |
| 5 | 360 |
| 6 | 2880 |
| 7 | 20160 |
| 8 | 201600 |
| 9 | 1814400 |
| 10 | 21772800 |
| 11 | 239500800 |
| 12 | 3353011200 |
| 13 | 43589145600 |
| 14 | 697426329600 |
| 15 | 10461394944000 |
| 16 | 188305108992000 |
| 17 | 3201186852864000 |
| 18 | 64023737057280000 |
| 19 | 1216451004088320000 |
| 20 | 26761922089943040000 |
| 21 | 562000363888803840000 |