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) |
|---|---|
| 4 | 0 |
| 5 | 1 |
| 6 | 172 |
| 7 | 17041 |
| 8 | 1382400 |
| 9 | 104454120 |
| 10 | 7801139200 |
| 11 | 593322510704 |
| 12 | 46672464052224 |
| 13 | 3827977546598400 |
| 14 | 328664453612830720 |
| 15 | 29590252898580000000 |
| 16 | 2794588822832496508928 |
| 17 | 276747699113763664091136 |
| 18 | 28712738456619366481920000 |
| 19 | 3117500646133634877355274240 |
| 20 | 353783948741967872000000000000 |