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 | 2 |
| 2 | -6 |
| 3 | 24 |
| 4 | -80 |
| 5 | 450 |
| 6 | -2142 |
| 7 | 17696 |
| 8 | -112464 |
| 9 | 1232370 |
| 10 | -9761510 |
| 11 | 132951192 |
| 12 | -1258797696 |
| 13 | 20476388114 |
| 14 | -225380451870 |
| 15 | 4261074439680 |
| 16 | -53438049741152 |
| 17 | 1151146814425506 |
| 18 | -16199301256675974 |
| 19 | 391615698778725080 |
| 20 | -6109914386833902960 |