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 | -1 |
| 2 | -2 |
| 3 | 0 |
| 4 | 6 |
| 5 | 90 |
| 6 | 240 |
| 7 | 2100 |
| 8 | 1680 |
| 9 | -28560 |
| 10 | -682080 |
| 11 | -7835520 |
| 12 | -134497440 |
| 13 | -1059458400 |
| 14 | -13047914880 |
| 15 | -138646347840 |
| 16 | -1130671301760 |
| 17 | 3558932657280 |
| 18 | 93341485036800 |
| 19 | 7903311136680960 |
| 20 | 149238605943947520 |
| 21 | 3997338754242113280 |
| 22 | 86934078099901992960 |