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 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 21 |
| 4 | 232 |
| 5 | 3005 |
| 6 | 45936 |
| 7 | 818503 |
| 8 | 16736896 |
| 9 | 387057609 |
| 10 | 9996371200 |
| 11 | 285271753811 |
| 12 | 8915621446656 |
| 13 | 302868879571453 |
| 14 | 11111919647266816 |
| 15 | 437892582706491375 |
| 16 | 18446723150919663616 |
| 17 | 827239906198908668177 |
| 18 | 39346401672922831847424 |
| 19 | 1978419534015213180291979 |