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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 24 |
| 5 | 96 |
| 6 | 1080 |
| 7 | 6480 |
| 8 | 80640 |
| 9 | 645120 |
| 10 | 9072000 |
| 11 | 90720000 |
| 12 | 1437004800 |
| 13 | 17244057600 |
| 14 | 305124019200 |
| 15 | 4271736268800 |
| 16 | 83691159552000 |
| 17 | 1339058552832000 |
| 18 | 28810681675776000 |
| 19 | 518592270163968000 |
| 20 | 12164510040883200000 |