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) |
|---|---|
| 3 | 0 |
| 4 | 3 |
| 5 | 15 |
| 6 | 45 |
| 7 | 315 |
| 8 | 3150 |
| 9 | 28350 |
| 10 | 274050 |
| 11 | 3014550 |
| 12 | 36330525 |
| 13 | 472296825 |
| 14 | 6609317715 |
| 15 | 99139765725 |
| 16 | 1586293008300 |
| 17 | 26966981141100 |
| 18 | 485404420000500 |
| 19 | 9222683980009500 |
| 20 | 184453709062998375 |