%I A107680
%S A107680 1,1,4,4,4,4,13,13,13,13,13,13,13,13,40,40,40,40,40,40,40,40,40,40,40,
%T A107680 40,40,40,40,40,121,121,121,121,121,121,121,121,121,121,121,121,121,121,
%U A107680 121,121,121,121,121,121,121,121,121,121,121,121,121,121,121,121,121
%N A107680 Repeating k-th ternary repunit 2^k times for k>0.
%C A107680 A032924(n) = a(n) + A107681(n);
%C A107680 a(n) = greatest ternary repunit that is not greater than the n-th number 
               with no 2 in ternary representation;
%C A107680 A081604(A107681(n)) <= A081604(a(n)) = A081604(A032924(n)) = A000523(n+1).
%F A107680 a(n) = A003462(A000523(n+1)).
%e A107680 k=1: A003462(1) = (3^1-1)/2 = 1, therefore a(1) = a(2^1) = 1;
%e A107680 k=2: A003462(2) = (3^2-1)/2 = 4, therefore a(2+1) = a(2+2) =
%e A107680 a(2+3) = a(2+2^2) = 4.
%Y A107680 Cf. A007089.
%Y A107680 Sequence in context: A013189 A035621 A046109 this_sequence A134660 A132383 
               A115639
%Y A107680 Adjacent sequences: A107677 A107678 A107679 this_sequence A107681 A107682 
               A107683
%K A107680 nonn
%O A107680 1,3
%A A107680 Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), May 20 2005
%E A107680 Corrected by T. D. Noe (noe(AT)sspectra.com), Oct 25 2006