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.
?(# != {} && IntegerQ[Mean[#]] && IntegerQ[HarmonicMean[#]] &)]; Array[a, 20] (* _Amiram Eldar has authored 0 sequences.