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A231087 Number of perfect matchings in graph C_3 x C_{2n} 6
50, 224, 1058, 5054, 24200, 115934, 555458, 2661344, 12751250, 61094894, 292723208, 1402521134, 6719882450, 32196891104, 154264573058, 739125974174, 3541365297800, 16967700514814, 81297137276258, 389517985866464, 1866292792056050, 8941945974413774, 42843437080012808, 205275239425650254 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

LINKS

Table of n, a(n) for n=2..25.

Index entries for sequences related to dominoes

Index entries for linear recurrences with constant coefficients, signature (6, -6, 1)

FORMULA

a(n) = 2*(((sqrt(7)+sqrt(3))/2)^n + ((sqrt(7)-sqrt(3))/2)^n)^2.

G.f.: 2*x^2*(25-38*x+7*x^2)/((1-x)*(1-5*x+x^2)).

PROG

(PARI) Vec(2*x^2*(25-38*x+7*x^2)/((1-x)*(1-5*x+x^2))+O(x^66)) \\ Joerg Arndt, Nov 03 2013

CROSSREFS

Cf. A220864.

Sequence in context: A186843 A250527 A251065 * A235956 A197971 A235567

Adjacent sequences:  A231084 A231085 A231086 * A231088 A231089 A231090

KEYWORD

easy,nonn

AUTHOR

Sergey Perepechko, Nov 03 2013

STATUS

approved

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)