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 | 24 |
| 4 | 300 |
| 5 | 4260 |
| 6 | 69120 |
| 7 | 1271340 |
| 8 | 26233200 |
| 9 | 601246800 |
| 10 | 15171105600 |
| 11 | 418203324000 |
| 12 | 12509695598400 |
| 13 | 403696590897600 |
| 14 | 13982667790291200 |
| 15 | 517482647165484000 |
| 16 | 20381726051118432000 |
| 17 | 851302665544050720000 |
| 18 | 37587618060140244096000 |
| 19 | 1749369290830388555328000 |
| 20 | 85599487854917373617280000 |