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%I A269869 #20 Jun 19 2017 09:27:57
%S A269869 1,4,27,425,14278,1054396,169858667,59811185171,46012925161519,
%T A269869 77344464552678876,284066030784415134855,2279568155737623235728996,
%U A269869 39969481180418160836567285156,1531253921482570179838977438893104,128176575381689893022287259560629125869
%N A269869 Number of matchings (not necessarily perfect) in the triangle graph of order n.
%C A269869 The triangle graph of order n has n rows with i vertices in row i. Each vertex is connected to the neighbors in the same row and up to two vertices in each of the neighboring rows. The graph has A000217(n) vertices and 3*A000217(n-1) edges altogether.
%H A269869 Andrew Howroyd, <a href="/A269869/b269869.txt">Table of n, a(n) for n = 1..25</a>
%H A269869 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/IndependentEdgeSet.html">Independent Edge Set</a>
%H A269869 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Matching.html">Matching</a>
%H A269869 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/TriangularGridGraph.html">Triangular Grid Graph</a>
%Y A269869 Cf. A000217, A028420, A039907, A112676, A178446.
%Y A269869 Row sums of A288852.
%K A269869 nonn
%O A269869 1,2
%A A269869 _Andrew Howroyd_, Mar 06 2016

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