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 | 12 |
| 4 | 96 |
| 5 | 720 |
| 6 | 6480 |
| 7 | 60480 |
| 8 | 645120 |
| 9 | 7257600 |
| 10 | 90720000 |
| 11 | 1197504000 |
| 12 | 17244057600 |
| 13 | 261534873600 |
| 14 | 4271736268800 |
| 15 | 73229764608000 |
| 16 | 1339058552832000 |
| 17 | 25609494822912000 |
| 18 | 518592270163968000 |
| 19 | 10948059036794880000 |
| 20 | 243290200817664000000 |