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 | 2 |
| 2 | -24 |
| 3 | 720 |
| 4 | -40320 |
| 5 | 3628800 |
| 6 | -479001600 |
| 7 | 87178291200 |
| 8 | -20922789888000 |
| 9 | 6402373705728000 |
| 10 | -2432902008176640000 |
| 11 | 1124000727777607680000 |
| 12 | -620448401733239439360000 |
| 13 | 403291461126605635584000000 |
| 14 | -304888344611713860501504000000 |
| 15 | 265252859812191058636308480000000 |