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 | 4 |
| 3 | 24 |
| 4 | 176 |
| 5 | 1456 |
| 6 | 13056 |
| 7 | 124032 |
| 8 | 1230592 |
| 9 | 12629760 |
| 10 | 133186560 |
| 11 | 1436098560 |
| 12 | 15774990336 |
| 13 | 176028860416 |
| 14 | 1990947110912 |
| 15 | 22783499599872 |
| 16 | 263411369705472 |
| 17 | 3073132646563840 |
| 18 | 36143187370967040 |
| 19 | 428157758086840320 |
| 20 | 5105072641718353920 |
| 21 | 61228492804372561920 |