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 | 24 |
| 5 | -380 |
| 6 | 720 |
| 7 | 31794 |
| 8 | -361088 |
| 9 | -2104056 |
| 10 | 101548800 |
| 11 | -612792290 |
| 12 | -25534891008 |
| 13 | 593660731404 |
| 14 | 2831189530624 |
| 15 | -361541172525750 |
| 16 | 4481749181890560 |
| 17 | 169464194149739536 |
| 18 | -6805365045197340672 |
| 19 | -9663483091971306186 |
| 20 | 6883830206467440640000 |