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 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | -20 |
| 6 | 420 |
| 7 | -252 |
| 8 | -336 |
| 9 | 66960 |
| 10 | -368640 |
| 11 | 2328480 |
| 12 | 2898720 |
| 13 | -117767520 |
| 14 | 1720764864 |
| 15 | -12297479040 |
| 16 | 58230547200 |
| 17 | 312819736320 |
| 18 | -9239378296320 |
| 19 | 128087696977920 |
| 20 | -1154590730496000 |
| 21 | 7050771080478720 |
| 22 | 398679450301440 |
| 23 | -591762353886950400 |
| 24 | 6580219687752775680 |