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 A031952 #13 Aug 10 2021 17:11:51 %S A031952 7,9,10,11,12,13,14,15,17,18,19,20,21,22,23,25,26,27,28,29,30,31,33, %T A031952 34,35,36,37,38,39,41,42,43,44,45,46,47,49,50,56,58,59,60,61,62,64,65, %U A031952 71,73,78,81,85,89,92,97,98,100,106,107,112,113 %N A031952 Numbers with exactly two distinct base-7 digits. %Y A031952 Cf. A007093. %K A031952 nonn,base %O A031952 1,1 %A A031952 _Clark Kimberling_