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 | 130 |
| 7 | -720 |
| 8 | 8505 |
| 9 | -35840 |
| 10 | 412776 |
| 11 | -3628800 |
| 12 | 42030450 |
| 13 | -479001600 |
| 14 | 7019298000 |
| 15 | -82614884352 |
| 16 | 1886805545625 |
| 17 | -20922789888000 |
| 18 | 374426276224000 |
| 19 | -6402373705728000 |
| 20 | 134987215801622184 |
| 21 | -2379913632645120000 |
| 22 | 55685679780013920000 |