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A220868
Number of perfect matchings in the twisted graph (C_4 X C_n)_{(13)(24)}.
1
3, 24, 54, 260, 726, 3096, 10086, 39940, 140454, 537624, 1956246, 7379204, 27246966, 102144024, 379501254, 1418981380, 5285770566, 19742287896, 73621286646, 274848860420
OFFSET
1,1
LINKS
S. Butler and S. Osborne, Counting tilings by taking walks, 2012.
FORMULA
Empirical g.f.: -x * (3*x^7 - 5*x^6 - 33*x^5 + 27*x^4 + 61*x^3 + 45*x^2 - 15*x - 3) / ( (x + 1) * (x^2 - 4*x + 1) * (x^2 - 2*x - 1) * (x^2 + 2*x - 1) ). - Joerg Arndt, Nov 17 2015
CROSSREFS
Sequence in context: A293594 A160665 A211034 * A296273 A101008 A070734
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 27 2012
EXTENSIONS
a(1)-a(2),a(11)-a(20) from Andrew Howroyd, Nov 15 2015
STATUS
approved