OFFSET
0,4
COMMENTS
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
REFERENCES
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).
LINKS
J. Propp, Updated article
J. Propp, Enumeration of matchings: problems and progress, in L. J. Billera et al. (eds.), New Perspectives in Algebraic Combinatorics
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, May 28 2002
EXTENSIONS
a(19)-a(24) from Andrew Howroyd, Mar 06 2016
STATUS
approved