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 | 2 |
| 1 | 1 |
| 2 | 6 |
| 3 | 24 |
| 4 | 168 |
| 5 | 1320 |
| 6 | 12960 |
| 7 | 146160 |
| 8 | 1895040 |
| 9 | 27578880 |
| 10 | 446342400 |
| 11 | 7943443200 |
| 12 | 154238515200 |
| 13 | 3244277836800 |
| 14 | 73491299481600 |
| 15 | 1783667837952000 |
| 16 | 46176597282816000 |
| 17 | 1270159805730816000 |
| 18 | 36992915271696384000 |
| 19 | 1137260043722170368000 |
| 20 | 36802508677688033280000 |