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 | 3 |
| 2 | -240 |
| 3 | -6497 |
| 4 | -65280 |
| 5 | -389601 |
| 6 | -1675520 |
| 7 | -5748417 |
| 8 | -16711680 |
| 9 | -42784577 |
| 10 | -98951424 |
| 11 | -210164577 |
| 12 | -413204480 |
| 13 | -748621857 |
| 14 | -1207353600 |
| 15 | -1489148801 |
| 16 | 0 |
| 17 | 10204111743 |
| 18 | 57699516160 |
| 19 | 257894343903 |
| 20 | 1073911627776 |