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 | 0 |
| 2 | -2 |
| 3 | 6 |
| 4 | -12 |
| 5 | 0 |
| 6 | 240 |
| 7 | -2520 |
| 8 | 21840 |
| 9 | -181440 |
| 10 | 1481760 |
| 11 | -11642400 |
| 12 | 80498880 |
| 13 | -311351040 |
| 14 | -4739454720 |
| 15 | 183437654400 |
| 16 | -4300276780800 |
| 17 | 88851284121600 |
| 18 | -1754954007206400 |
| 19 | 34107089784768000 |
| 20 | -659574028252339200 |
| 21 | 12724865943229440000 |
| 22 | -244046146272658329600 |