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 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 0 |
| 7 | 0 |
| 8 | 0 |
| 9 | 40320 |
| 10 | 3628800 |
| 11 | 219542400 |
| 12 | 11496038400 |
| 13 | 570031862400 |
| 14 | 27908676956160 |
| 15 | 1379187810000000 |
| 16 | 69648048665395200 |
| 17 | 3619848890071814400 |
| 18 | 194428045753727385600 |
| 19 | 10817313676715756770560 |
| 20 | 624148118196535296000000 |
| 21 | 37365232440634029661766400 |