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 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 8 |
| 5 | 40 |
| 6 | 180 |
| 7 | 140 |
| 8 | 896 |
| 9 | 72576 |
| 10 | 604800 |
| 11 | 6652800 |
| 12 | 68428800 |
| 13 | 59304960 |
| 14 | 726485760 |
| 15 | 163459296000 |
| 16 | 2324754432000 |
| 17 | 39520825344000 |
| 18 | 640237370572800 |
| 19 | 579262382899200 |
| 20 | 10532043325440000 |
| 21 | 4644631106519040000 |