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 A039001 #20 Jun 26 2021 06:45:05 %S A039001 0,5,7,11,15,19,21,29,33,44,45,50,52,55,57,63,68,70,76,83,87,98,99, %T A039001 104,106,116,128,132,135,140,142,146,150,154,156,163,165,171,176,178, %U A039001 184,189,194,196,200,204,208,210,220,226,228,245,249,260,261,266,268 %N A039001 Numbers whose base-3 representation has the same number of 1's and 2's. %H A039001 Daniel Starodubtsev, <a href="/A039001/b039001.txt">Table of n, a(n) for n = 1..10000</a> %o A039001 (PARI) isok(m) = my(d=digits(m, 3)); #select(x->(x==1), d) == #select(x->(x==2), d); \\ _Michel Marcus_, Mar 23 2020 %Y A039001 Cf. A007089, A062756, A081603. %K A039001 nonn,base,easy %O A039001 1,2 %A A039001 _Olivier Gérard_