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A051929
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Number of independent sets of vertices in graph K_4 X C_n (n > 2).
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2
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5, 1, 21, 73, 325, 1361, 5781, 24473, 103685, 439201, 1860501, 7881193, 33385285, 141422321, 599074581, 2537720633, 10749957125, 45537549121, 192900153621, 817138163593, 3461452808005, 14662949395601, 62113250390421, 263115950957273, 1114577054219525
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OFFSET
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0,1
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LINKS
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FORMULA
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a(n) = 3*a(n-1) + 5*a(n-2) + a(n-3).
a(n) = (3*(-1)^n+(2-sqrt(5))^n+(2+sqrt(5))^n).
G.f.: (5 - 14*x - 7*x^2) / ((1 + x)*(1 - 4*x - x^2)).
(End)
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PROG
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(PARI) Vec((5 - 14*x - 7*x^2) / ((1 + x)*(1 - 4*x - x^2)) + O(x^30)) \\ Colin Barker, May 11 2017
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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