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 | 2 |
| 3 | 9 |
| 4 | 56 |
| 5 | 450 |
| 6 | 4464 |
| 7 | 52920 |
| 8 | 731520 |
| 9 | 11566800 |
| 10 | 206035200 |
| 11 | 4083488640 |
| 12 | 89137843200 |
| 13 | 2124970848000 |
| 14 | 54929029478400 |
| 15 | 1530259226496000 |
| 16 | 45705137084006400 |
| 17 | 1456873475016960000 |
| 18 | 49362677881380864000 |