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 | 0 |
| 4 | 6 |
| 5 | 40 |
| 6 | 260 |
| 7 | 1848 |
| 8 | 14616 |
| 9 | 128448 |
| 10 | 1246752 |
| 11 | 13273920 |
| 12 | 153996480 |
| 13 | 1935048960 |
| 14 | 26193473280 |
| 15 | 380120670720 |
| 16 | 5888620684800 |
| 17 | 97007636275200 |
| 18 | 1693590745190400 |
| 19 | 31237853849395200 |
| 20 | 607035345406156800 |