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 | 3 |
| 4 | 12 |
| 5 | 40 |
| 6 | 120 |
| 7 | 336 |
| 8 | 7168 |
| 9 | 58752 |
| 10 | 345600 |
| 11 | 1682560 |
| 12 | 15983616 |
| 13 | 142192128 |
| 14 | 2318697472 |
| 15 | 25614382080 |
| 16 | 282753361920 |
| 17 | 2645093410816 |
| 18 | 48869743454208 |
| 19 | 674729909839872 |
| 20 | 12153962014842880 |
| 21 | 167314499427532800 |
| 22 | 1986101341059956736 |
| 23 | 20335611320801886208 |