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 | 3 |
| 3 | 23 |
| 4 | 164 |
| 5 | 1252 |
| 6 | 10512 |
| 7 | 97344 |
| 8 | 990432 |
| 9 | 11010528 |
| 10 | 132966720 |
| 11 | 1734793920 |
| 12 | 24330205440 |
| 13 | 365150833920 |
| 14 | 5840673108480 |
| 15 | 99204809356800 |
| 16 | 1783428104908800 |
| 17 | 33833306484633600 |
| 18 | 675513065777356800 |
| 19 | 14160039606855475200 |
| 20 | 310935875030323200000 |