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.
?(FreeQ[#,0]&&AllTrue[Sqrt[#],IntegerQ]&)]==4; Select[Range[7500],nz4Q] (* _Harvey P. Dale has authored 0 sequences.