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 A083904 #17 Jun 27 2021 07:53:38
%S A083904 0,1,0,4,3,1,0,13,12,10,9,4,3,1,0,40,39,37,36,31,30,28,27,13,12,10,9,
%T A083904 4,3,1,0,121,120,118,117,112,111,109,108,94,93,91,90,85,84,82,81,40,
%U A083904 39,37,36,31,30,28,27,13,12,10,9,4,3,1,0,364,363,361,360
%N A083904 G.f. 1/(1-x) * Sum_{k>=0} 3^k * x^2^(k+1)/(1+x^2^k).
%C A083904 Distance to next number of form 2^k-1, written down in binary, then interpreted as ternary. Thus the numbers have no 2 in ternary representation.
%H A083904 Ralf Stephan, <a href="/somedcgf.html">Some divide-and-conquer sequences with (relatively) simple ordinary generating functions</a>.
%H A083904 Ralf Stephan, <a href="/A079944/a079944.ps">Table of generating functions</a>
%F A083904 a(1)=0, a(2n) = 3a(n)+1, a(2n+1) = 3a(n).
%F A083904 a(n) = (1/2)*(3^(floor(log_2(n))+1)-1) - A005836(n).
%o A083904 (PARI) for(n=1, 100, l=ceil(log(n)/log(2)); t=polcoeff(1/(1-x)*sum(k=0, l, 3^k*(x^2^(k+1))/(1+x^2^k)) + O(x^(n+1)), n); print1(t", "))
%Y A083904 Cf. A005823, A005836.
%K A083904 nonn,easy
%O A083904 1,4
%A A083904 _Ralf Stephan_, Jun 18 2003