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 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 24 |
| 5 | 360 |
| 6 | 4320 |
| 7 | 45360 |
| 8 | 435456 |
| 9 | 3919104 |
| 10 | 33592320 |
| 11 | 277136640 |
| 12 | 2217093120 |
| 13 | 17293326336 |
| 14 | 132058128384 |
| 15 | 990435962880 |
| 16 | 7313988648960 |
| 17 | 53287631585280 |
| 18 | 383670947414016 |
| 19 | 2733655500324864 |
| 20 | 19296391766999040 |
| 21 | 135074742368993280 |