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 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 24 |
| 6 | 190 |
| 7 | 1260 |
| 8 | 7602 |
| 9 | 43344 |
| 10 | 238308 |
| 11 | 1278360 |
| 12 | 6739590 |
| 13 | 35086392 |
| 14 | 180952200 |
| 15 | 926583840 |
| 16 | 4718481950 |
| 17 | 23923888800 |
| 18 | 120881319280 |
| 19 | 609086170080 |
| 20 | 3062089990710 |
| 21 | 15365797583400 |
| 22 | 76989505040350 |
| 23 | 385265732393388 |