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 | 120 |
| 6 | 1800 |
| 7 | 16800 |
| 8 | 126000 |
| 9 | 834120 |
| 10 | 6917400 |
| 11 | 129399600 |
| 12 | 3259080000 |
| 13 | 72252300120 |
| 14 | 1370602233000 |
| 15 | 23218349918400 |
| 16 | 377834084082000 |
| 17 | 6709735404918120 |
| 18 | 147369456297228600 |
| 19 | 3899127761438053200 |
| 20 | 109421543771265852000 |
| 21 | 3002806840023201408120 |