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 | 14 |
| 5 | 64 |
| 6 | 426 |
| 7 | 2790 |
| 8 | 24024 |
| 9 | 229080 |
| 10 | 2399760 |
| 11 | 25022880 |
| 12 | 312273360 |
| 13 | 3884393520 |
| 14 | 56255149440 |
| 15 | 869007242880 |
| 16 | 14266826784000 |
| 17 | 233845982899200 |
| 18 | 4309095479673600 |
| 19 | 79300508301907200 |
| 20 | 1620482929875532800 |
| 21 | 34699018357638835200 |
| 22 | 777011144137311283200 |