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 A258410 #9 Feb 06 2017 14:37:50 %S A258410 4,5,18,20,21,24,25,27,70,74,76,77,82,84,85,88,89,91,98,100,101,104, %T A258410 105,107,112,113,115,119,270,278,282,284,285,294,298,300,301,306,308, %U A258410 309,312,313,315,326,330,332,333,338,340,341,344,345,347,354,356,357 %N A258410 Nonnegative integers with an equal number of occurrences of all digits in bijective base-2 numeration. %H A258410 Alois P. Heinz, <a href="/A258410/b258410.txt">Table of n, a(n) for n = 1..10000</a> %H A258410 Wikipedia, <a href="https://en.wikipedia.org/wiki/Bijective_numeration">Bijective numeration</a> %e A258410 4 = 12_bij2, 5 = 21_bij2, 18 = 1122_bij2, 20 = 1212_bij2. %p A258410 p:= proc(n) local d, m, r; m:= n; r:= 0; %p A258410 while m>0 do d:= irem(m, 2, 'm'); %p A258410 if d=0 then d:=2; m:= m-1 fi; %p A258410 r:= r+x^d %p A258410 od; %p A258410 simplify(r/(x+x^2))::integer %p A258410 end: %p A258410 a:= proc(n) option remember; local k; %p A258410 for k from 1+`if`(n=1, 0, a(n-1)) by 1 %p A258410 while not p(k) do od; k %p A258410 end: %p A258410 seq(a(n), n=1..70); %Y A258410 Cf. A007931, A214676, A257869, A258411. %K A258410 nonn,base %O A258410 1,1 %A A258410 _Alois P. Heinz_, May 29 2015