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Number of P-graphs with vertical symmetry.
(Formerly M2854)
1

%I M2854 #15 Nov 08 2017 08:46:46

%S 1,3,10,39,158,674,2944,13191,60078,277890,1300536,6151078,29346036,

%T 141088632,682825140,3324172359,16267134462,79975707362,394833880540,

%U 1956620531762,9729300574580,48529814786620,242757311049680,1217508537475894

%N Number of P-graphs with vertical symmetry.

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H R. C. Read, <a href="http://dx.doi.org/10.1007/BF02188172">On the enumeration of a class of plane multigraphs</a>, Aequat. Math. 31 (1986) no 1, 47-63.

%F a(n) = coefficient of x^(2*n) in D(x)^2 / (1-D(x)^2) where D(x) = Sum_{k=0..infinity} A007162(k) * x^(2*k+1). - _Sean A. Irvine_, Nov 06 2017

%Y Cf. A007162.

%K nonn

%O 1,2

%A _N. J. A. Sloane_

%E a(9)-a(10) corrected and more terms from _Sean A. Irvine_, Nov 06 2017