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A267799
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a(n) = (1 + 2^n + 3^n)/2.
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1
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3, 7, 18, 49, 138, 397, 1158, 3409, 10098, 30037, 89598, 267769, 801258, 2399677, 7190838, 21556129, 64635618, 193841317, 581392878, 1743916489, 5231225178, 15692626957, 47075783718, 141223156849, 423661081938, 1270966468597, 3812865851358, 11438530445209, 34315457117898, 102946102918237
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = 6*a(n-1)-11*a(n-2)+6*a(n-3) for n>3.
G.f.: x*(3-11*x+9*x^2) / ((1-x)*(1-2*x)*(1-3*x)).
(End)
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EXAMPLE
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a(3) = (1 + 2^3 + 3^3)/2 = 18.
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MATHEMATICA
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PROG
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(PARI) Vec(x*(3-11*x+9*x^2)/((1-x)*(1-2*x)*(1-3*x)) + O(x^50)) \\ Colin Barker, Apr 07 2016
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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