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 | 15 |
| 4 | 104 |
| 5 | 770 |
| 6 | 6264 |
| 7 | 56196 |
| 8 | 554112 |
| 9 | 5973264 |
| 10 | 69998400 |
| 11 | 886897440 |
| 12 | 12089295360 |
| 13 | 176484597120 |
| 14 | 2748022986240 |
| 15 | 45472329504000 |
| 16 | 796983880089600 |
| 17 | 14751208762214400 |
| 18 | 287543058350284800 |