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 | 1 |
| 2 | 0 |
| 3 | 2 |
| 4 | 4 |
| 5 | 36 |
| 6 | 144 |
| 7 | 1440 |
| 8 | 8640 |
| 9 | 100800 |
| 10 | 806400 |
| 11 | 10886400 |
| 12 | 108864000 |
| 13 | 1676505600 |
| 14 | 20118067200 |
| 15 | 348713164800 |
| 16 | 4881984307200 |
| 17 | 94152554496000 |
| 18 | 1506440871936000 |
| 19 | 32011868528640000 |
| 20 | 576213633515520000 |
| 21 | 13380961044971520000 |
| 22 | 267619220899430400000 |