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%I #14 Mar 11 2016 14:19:03
%S 1,0,0,3,6,0,0,1065,6276,0,0,45949563,807343128,0,0,221797080594801,
%T 11812299253803024,0,0,117066491250943949567763,
%U 19100803250397148607852640,0,0,6685924427990669481186818442889689,3366736732994780307970181864980219968
%N Number of perfect matchings in variant of right triangle graph with n edges.
%C The graph consists of the vertices (x,y) where 0<=y<=x<n. Vertices (x1,y1) and (x2,y2) are adjacent iff x1=x2 and |y1-y2|=1 or |x1-x2|=1 and y1=y2 or |x1-x2|=|y1-y2|=1 and x1+y1 is even (all horizontal, all vertical and some diagonal). - _Andrew Howroyd_, Mar 06 2016
%D J. Propp, Enumeration of matchings: problems and progress, pp. 255-291 in L. J. Billera et al., eds, New Perspectives in Algebraic Combinatorics, Cambridge, 1999 (see Problem 29).
%H J. Propp, <a href="http://faculty.uml.edu/jpropp/update.pdf">Updated article</a>
%H J. Propp, Enumeration of matchings: problems and progress, in L. J. Billera et al. (eds.), <a href="http://www.msri.org/publications/books/Book38/contents.html">New Perspectives in Algebraic Combinatorics</a>
%Y Cf. A071106.
%K nonn
%O 0,4
%A _N. J. A. Sloane_, May 28 2002
%E a(19)-a(24) from _Andrew Howroyd_, Mar 06 2016
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