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 | 1 |
| 3 | 6 |
| 4 | 36 |
| 5 | 240 |
| 6 | 1698 |
| 7 | 14304 |
| 8 | 118800 |
| 9 | 1118160 |
| 10 | 11705288 |
| 11 | 144092256 |
| 12 | 1738439808 |
| 13 | 24817158912 |
| 14 | 355309325280 |
| 15 | 5378578601760 |
| 16 | 86081749397280 |
| 17 | 1570394279039040 |
| 18 | 28281459220193088 |
| 19 | 572031558109589760 |
| 20 | 11458497230555094720 |