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 | 1 |
| 5 | 25 |
| 6 | 450 |
| 7 | 7350 |
| 8 | 117600 |
| 9 | 1905120 |
| 10 | 31752000 |
| 11 | 548856000 |
| 12 | 9879408000 |
| 13 | 185513328000 |
| 14 | 3636061228800 |
| 15 | 74373979680000 |
| 16 | 1586644899840000 |
| 17 | 35272336619520000 |
| 18 | 816302647480320000 |
| 19 | 19645683716026368000 |
| 20 | 491142092900659200000 |
| 21 | 12740803704070041600000 |