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 | 3 |
| 4 | -13 |
| 5 | 77 |
| 6 | -576 |
| 7 | 5219 |
| 8 | -55567 |
| 9 | 680028 |
| 10 | -9405302 |
| 11 | 145067040 |
| 12 | -2468571128 |
| 13 | 45936991110 |
| 14 | -927915150852 |
| 15 | 20219040931738 |
| 16 | -472697857817078 |
| 17 | 11801903989774760 |
| 18 | -313395752536945568 |
| 19 | 8819464678850030936 |
| 20 | -262185434197432956664 |
| 21 | 8210080944919085511680 |