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A071105 Number of perfect matchings in variant of right triangle graph with n edges. 1
1, 0, 0, 3, 6, 0, 0, 1065, 6276, 0, 0, 45949563, 807343128, 0, 0, 221797080594801, 11812299253803024, 0, 0, 117066491250943949567763, 19100803250397148607852640, 0, 0, 6685924427990669481186818442889689, 3366736732994780307970181864980219968 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=0..24.

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

Cf. A071106.

Sequence in context: A175645 A178514 A154924 * A218113 A295194 A104613

Adjacent sequences:  A071102 A071103 A071104 * A071106 A071107 A071108

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, May 28 2002

EXTENSIONS

a(19)-a(24) from Andrew Howroyd, Mar 06 2016

STATUS

approved

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Last modified October 18 04:54 EDT 2019. Contains 328145 sequences. (Running on oeis4.)