%I #10 Jan 27 2014 17:17:45

%S 0,1,1,2,1,3,5,5,6,3,6,4,4,5,7,5,8,2,2,3,7,8,5,11,11,12,10,8,6,7,9,8,

%T 7,10,9,9,10,10,11,13,6,8,8,9,11,14,14,15,17,18,9,12,11,15,18,10,12,

%U 12,13,7,11,16,17,19,12,14,16,18,11,17,20,9,13,8,10,13,9,14,17,22,14,18,12,15

%N Working in base 3, a(n+1) = number of preceding terms that are contained in a(n); a(0)=0.

%C a(A137656(n)) = n and a(m) <> n for m < A137656(n).

%H R. Zumkeller, <a href="/A137655/b137655.txt">Table of n, a(n) for n = 0..25000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Ternary.html">Ternary</a>

%e a(15)=#{a(1),a(2),a(3),a(4),a(14)}=5;

%e a(16)=#{a(1),a(2),a(3),a(4),a(6),a(7),a(13),a(15)}=8;

%e a(17)=#{a(3),a(16)}=2.

%Y Cf. A007089, A131813.

%K nonn,base,hear,look

%O 0,4

%A _Reinhard Zumkeller_, Feb 01 2008