%I A000985 M2907 N1168
%S A000985 1,1,3,11,56,348,2578,22054,213798,2313638,27627434,360646314,5107177312,
%T A000985 77954299144,1275489929604,22265845018412,412989204564572,8109686585668956,
%U A000985 168051656468233972,3664479286118269972,83868072451846938336,2009964340465840802576
%N A000985 Number of n X n symmetric matrices with nonnegative entries and all row 
               sums 2.
%D A000985 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A000985 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A000985 H. Gupta, Enumeration of symmetric matrices, Duke Math. J., 35 (1968), 
               653-659.
%D A000985 R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see 
               Example 5.2.7.
%H A000985 T. D. Noe, <a href="b000985.txt">Table of n, a(n) for n=0..100</a>
%H A000985 P. Flajolet and R. Sedgewick, <a href="http://algo.inria.fr/flajolet/
               Publications/books.html">Analytic Combinatorics</a>, 2009; see page 
               584
%F A000985 E.g.f.: (1-x)^(-1/2)*exp(x^2/4 + x/((2*(1-x)))).
%Y A000985 Cf. A000986.
%Y A000985 Sequence in context: A136104 A007841 A036760 this_sequence A094611 A052442 
               A001586
%Y A000985 Adjacent sequences: A000982 A000983 A000984 this_sequence A000986 A000987 
               A000988
%K A000985 nonn,nice,easy
%O A000985 0,3
%A A000985 N. J. A. Sloane (njas(AT)research.att.com).