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 | -3 |
| 4 | 24 |
| 5 | -20 |
| 6 | 720 |
| 7 | -630 |
| 8 | 4480 |
| 9 | -36288 |
| 10 | 3628800 |
| 11 | -3326400 |
| 12 | 479001600 |
| 13 | -444787200 |
| 14 | 5811886080 |
| 15 | -81729648000 |
| 16 | 20922789888000 |
| 17 | -19760412672000 |
| 18 | 6402373705728000 |
| 19 | -6082255020441600 |
| 20 | 115852476579840000 |
| 21 | -2322315553259520000 |
| 22 | 1124000727777607680000 |
| 23 | -1077167364120207360000 |