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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 24 |
| 5 | 240 |
| 6 | 1560 |
| 7 | 8400 |
| 8 | 81144 |
| 9 | 1638000 |
| 10 | 31058520 |
| 11 | 482499600 |
| 12 | 6905646264 |
| 13 | 114015261360 |
| 14 | 2456232531480 |
| 15 | 59734751403600 |
| 16 | 1427946773067384 |
| 17 | 33377481440110320 |
| 18 | 818549745973204440 |
| 19 | 22338800420915168400 |
| 20 | 667566534457962216504 |
| 21 | 20735588176755396824880 |