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 A043882 #11 Aug 25 2021 04:53:06 %S A043882 12,19,28,35,44,51,60,67,79,83,92,99,108,115,124,131,143,147,156,163, %T A043882 172,179,188,207,211,220,227,236,243,252,259,271,275,284,291,300,319, %U A043882 323,335,339,348,355,364,371,380,387,399,403 %N A043882 Numbers k such that 0 and 3 occur juxtaposed in the base-4 representation of k but not of k+1. %Y A043882 Cf. A007090. %K A043882 nonn,base %O A043882 1,1 %A A043882 _Clark Kimberling_