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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 0 |
| 4 | 6 |
| 5 | -22 |
| 6 | -30 |
| 7 | 952 |
| 8 | -5656 |
| 9 | -9952 |
| 10 | 508320 |
| 11 | -3874992 |
| 12 | -20690208 |
| 13 | 833780400 |
| 14 | -7697940432 |
| 15 | -52230156288 |
| 16 | 2467649024640 |
| 17 | -24686997151104 |
| 18 | -329724479772288 |
| 19 | 14493628861307136 |
| 20 | -159114034671287040 |
| 21 | -2682505451050592256 |
| 22 | 126421889770129637376 |