%I A007187 M2532
%S A007187 1,3,6,9,15,20,26,34,41
%N A007187 Leech's tree-labeling problem for n nodes.
%D A007187 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A007187 R. K. Guy, A quarter century of "Monthly" unsolved problems, 1969-1993, 
               Amer Math. Monthly, 100 (1993), 945-949.
%D A007187 R. K. Guy, Unsolved Problems in Number Theory, Sect. C10.
%D A007187 J. Leech, On the representation of $1,2,\cdots,n$ by differences. J. 
               London Math. Soc. 31 (1956), 160-169.
%H A007187 <a href="Sindx_Tra.html#trees">Index entries for sequences related to 
               trees</a>
%Y A007187 Cf. A005488.
%Y A007187 Sequence in context: A049991 A143981 A031940 this_sequence A082004 A112773 
               A070885
%Y A007187 Adjacent sequences: A007184 A007185 A007186 this_sequence A007188 A007189 
               A007190
%K A007187 nonn,hard,nice
%O A007187 2,2
%A A007187 N. J. A. Sloane (njas(AT)research.att.com).
%E A007187 a(11)>=48, a(12)>=55.