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 | 1 |
| 2 | 1 |
| 3 | -2 |
| 4 | 9 |
| 5 | -24 |
| 6 | 70 |
| 7 | -720 |
| 8 | 5985 |
| 9 | -39200 |
| 10 | 337176 |
| 11 | -3628800 |
| 12 | 40907790 |
| 13 | -479001600 |
| 14 | 6128488080 |
| 15 | -87104969952 |
| 16 | 1318070979225 |
| 17 | -20922789888000 |
| 18 | 354250929192160 |
| 19 | -6402373705728000 |
| 20 | 121882099274319384 |
| 21 | -2432849766865689600 |
| 22 | 51041047393559059200 |