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 A097089 #4 Mar 30 2012 18:36:41
%S A097089 0,0,1,2,2,4,6,4,8,7,11,12,13,13,14,15,18,18,20,22,23,24,26,26,25,26,
%T A097089 30,31,33,32,34,33,38,38,39,39,42,44,46,46,46,48,51,52,53,53,55,55,56,
%U A097089 55,59,61,62,63,65,66,68,68,70,71,73
%N A097089 Exponents of 2 that form the denominators of coefficients in function A(x) such that A(A(x)) = x+x^2.
%C A097089 A097088 lists the reduced numerators.
%F A097089 G.f.: A(x) = Sum_{n>=0} A097088(n)/2^a(n) where A(A(x)) = x + x^2.
%o A097089 (PARI) {a(n)=local(A,B,F=x+x^2+x*O(x^n));A=F; if(n==0,0, for(i=0,n,B=serreverse(A);A=(A+subst(B,x,F))/2); valuation(denominator(polcoeff(A,n,x)),2))}
%Y A097089 Cf. A097088.
%K A097089 nonn
%O A097089 0,4
%A A097089 _Paul D. Hanna_, Jul 23 2004