%I A130249
%S A130249 0,2,2,3,3,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
%T A130249 6,6,6,6,6,6,6,6,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
%U A130249 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8
%N A130249 Maximal index k of a Jacobsthal number such that A001045(k)<=n (the 'lower' 
               Jacobsthal inverse).
%C A130249 Inverse of the Jacobsthal sequence (A001045), nearly, since a(A001045(n))=n 
               except for n=1 (see A130250 for another version). a(n)+1 is equal 
               to the partial sum of the Jacobsthal indicator sequence (see A105348).
%F A130249 a(n)=floor(log_2(3n+1)). Also true: a(n)=A130250(n+1)-1=A130253(n)-1. 
               G.f.: g(x)=1/(1-x)*sum{k>=1, x^A001045(k)}.
%e A130249 a(12)=5, since A001045(5)=11<=12, but A001045(6)=21>12.
%Y A130249 For partial sums see A130251. Other related sequences A130250, A130253, 
               A105348. A001045, A130233, A130241.
%Y A130249 Sequence in context: A079730 A035486 A143489 this_sequence A061071 A122258 
               A068509
%Y A130249 Adjacent sequences: A130246 A130247 A130248 this_sequence A130250 A130251 
               A130252
%K A130249 nonn
%O A130249 0,2
%A A130249 Hieronymus Fischer (Hieronymus.Fischer(AT)gmx.de), May 20 2007