Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%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