%I A137747
%S A137747 0,0,0,0,0,0,0,1,7,34,143,555,2050,7343,25809
%N A137747 Number of different strings of length n obtained from "abcdefg" by iteratively 
               duplicating any substring.
%C A137747 See A137743 for more comments.
%H A137747 <a href="Sindx_Do.html#repeat">Index entries for doubling substrings</
               a>
%e A137747 a(k) = 0 for k<7, since no shorter string can be obtained by duplication 
               of substrings.
%e A137747 a(7) = 1 = # { abcdefg },
%e A137747 a(8) = 7 = # { aabcdefg, abbcdefg, abccdefg, abcddefg, abcdeefg, abcdeffg, 
               abcdefgg },
%e A137747 a(9) = 8*(8+1)/2-2 = 34: for each letter we have one string of the form 
               aaabcdefg;
%e A137747 for each 2-element subset {a,b}, {a,c},... we have the string with each 
               of these two letters duplicated (i.e. aabbcdefg, aabccdefg,...),
%e A137747 and for each of ab,bc,cd,...,fg we have the string with this substring 
               duplicated (ababcdefg,...,abcdefgfg).
%e A137747 (see A137746 for the pattern)
%o A137747 (PARI) A135473(14,7) /*function defined in A137743*/
%Y A137747 Cf. A137740-A137743, A135473, A137744-A137748.
%Y A137747 Sequence in context: A055852 A122611 A014915 this_sequence A005023 A094256 
               A094891
%Y A137747 Adjacent sequences: A137744 A137745 A137746 this_sequence A137748 A137749 
               A137750
%K A137747 more,nonn
%O A137747 0,9
%A A137747 M. F. Hasler (MHasler(AT)univ-ag.fr), Feb 10 2008