%I #6 Jan 21 2014 12:30:21
%S 1,0,2,0,3,1,4,0,5,2,6,1,7,3,8,9,9,7,10,34,11,36,12,136,13,190,14,567,
%T 15,1018,16,2445,17,5474,18,11371,19,28233,20,57961,21,143391,22,
%U 308793,23,740519,24,1668316
%N a(n) = number of strings of length n that can be obtained by starting with abc and repeatedly doubling any substring of length >= 2 in place.
%C A "weakly primitive" version of A135473. Cf. A135017.
%C Differs from A135017 in that the strings may contain repeated letters.
%H <a href="/index/Do#repeat">Index entries for doubling substrings</a>
%K nonn
%O 0,3
%A _David Applegate_ and _N. J. A. Sloane_, Feb 15 2008