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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 24 |
| 5 | 184 |
| 6 | 1672 |
| 7 | 17296 |
| 8 | 198800 |
| 9 | 2499200 |
| 10 | 33992000 |
| 11 | 496281344 |
| 12 | 7731823616 |
| 13 | 127946465280 |
| 14 | 2240485196800 |
| 15 | 41387447564800 |
| 16 | 804353715776000 |
| 17 | 16408115358117888 |
| 18 | 350584123058300928 |
| 19 | 7831051680901885952 |
| 20 | 182550106828365115392 |
| 21 | 4433782438058087202816 |
| 22 | 112031844502468602085376 |
| 23 | 2940834866411162315849728 |