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 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | 40 |
| 6 | 540 |
| 7 | 3528 |
| 8 | 25200 |
| 9 | 324000 |
| 10 | 3648960 |
| 11 | 41690880 |
| 12 | 622274400 |
| 13 | 9573033600 |
| 14 | 150465579264 |
| 15 | 2705877820800 |
| 16 | 51819600268800 |
| 17 | 1028013655818240 |
| 18 | 22086154437442560 |
| 19 | 504188626820659200 |
| 20 | 11997041025160396800 |
| 21 | 301999960230701322240 |