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 | 5 |
| 2 | 42 |
| 3 | 336 |
| 4 | 2640 |
| 5 | 20592 |
| 6 | 160160 |
| 7 | 1244672 |
| 8 | 9674496 |
| 9 | 75246080 |
| 10 | 585761792 |
| 11 | 4564377600 |
| 12 | 35602145280 |
| 13 | 277970595840 |
| 14 | 2172375244800 |
| 15 | 16992801914880 |
| 16 | 133035751833600 |
| 17 | 1042374243778560 |
| 18 | 8173537721057280 |
| 19 | 64136851016908800 |
| 20 | 503613708419727360 |
| 21 | 3956964851869286400 |