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 | 0 |
| 2 | 1 |
| 3 | 6 |
| 4 | 38 |
| 5 | 280 |
| 6 | 2538 |
| 7 | 27524 |
| 8 | 341912 |
| 9 | 4754880 |
| 10 | 73322360 |
| 11 | 1244282512 |
| 12 | 23048700912 |
| 13 | 462565343552 |
| 14 | 9996300546512 |
| 15 | 231444311970720 |
| 16 | 5715911385442688 |
| 17 | 149988948332148736 |
| 18 | 4167328800543910272 |
| 19 | 122218355207805620480 |
| 20 | 3773036019063284645120 |