%I A000137 M1625 N0636
%S A000137 1,2,6,18,58,186,614,2034,6818,22970,77858,264970,905294,3102434,
%T A000137 10661370,36722642,126752218,438294018,1518032598,5265341314,18286911130,
%U A000137 63586988434,221342104842,771235606050,2689688538646,9388096331642
%N A000137 Series-parallel numbers.
%D A000137 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A000137 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A000137 J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 
               142.
%F A000137 G.f.: (1+S)/(1-S), where S = g.f. for A000084.
%Y A000137 Cf. A036654, A036655, A058756, A000084.
%Y A000137 Sequence in context: A148458 A148459 A081057 this_sequence A151282 A157004 
               A085139
%Y A000137 Adjacent sequences: A000134 A000135 A000136 this_sequence A000138 A000139 
               A000140
%K A000137 nonn
%O A000137 1,2
%A A000137 N. J. A. Sloane (njas(AT)research.att.com).