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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | -1 |
| 4 | 18 |
| 5 | -86 |
| 6 | -210 |
| 7 | 8840 |
| 8 | -80080 |
| 9 | -266220 |
| 10 | 19991520 |
| 11 | -274725100 |
| 12 | -1006434000 |
| 13 | 123657316600 |
| 14 | -2328145274000 |
| 15 | -8148732243600 |
| 16 | 1621702497792000 |
| 17 | -39454300872662000 |
| 18 | -113331522571488000 |
| 19 | 38748502249144766000 |
| 20 | -1172806114215446464000 |
| 21 | -2126467491228525900000 |
| 22 | 1525200888587905488960000 |