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.
%I A037978 #9 Jul 16 2017 13:19:56 %S A037978 21,42,63,64,84,86,87,106,127,128,149,168,169,171,191,192,213,234,252, %T A037978 253,254,257,258,259,277,298,319,320,336,337,338,339,344,345,346,347, %U A037978 348,349,350,351,362,383,384,405,424,425,427 %N A037978 Numbers whose maximal base 4 run length is 3. %t A037978 Select[Range[500],Max[Length/@Split[IntegerDigits[#,4]]]==3&] (* _Harvey P. Dale_, Jul 16 2017 *) %Y A037978 Cf. A043278. %K A037978 nonn,base %O A037978 1,1 %A A037978 _Clark Kimberling_