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 | 2 |
| 3 | 14 |
| 4 | 48 |
| 5 | 424 |
| 6 | 3360 |
| 7 | 30288 |
| 8 | 276864 |
| 9 | 3591936 |
| 10 | 46241280 |
| 11 | 599212800 |
| 12 | 9205954560 |
| 13 | 142744412160 |
| 14 | 2554915184640 |
| 15 | 47649718609920 |
| 16 | 907617573273600 |
| 17 | 18296536869273600 |
| 18 | 413470794456760320 |
| 19 | 9130651338347642880 |
| 20 | 221996730181563187200 |