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A171507
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a(n) = (5*2^(n+1)-9-(-1)^n)/6-2*n.
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2
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0, 0, 1, 6, 17, 42, 93, 198, 409, 834, 1685, 3390, 6801, 13626, 27277, 54582, 109193, 218418, 436869, 873774, 1747585, 3495210, 6990461, 13980966, 27961977, 55924002, 111848053, 223696158, 447392369, 894784794, 1789569645, 3579139350, 7158278761, 14316557586
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OFFSET
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0,4
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LINKS
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FORMULA
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a(n) = 3*a(n-1)-a(n-2)-3*a(n-3)+2*a(n-4). G.f.: x^2*(1+3*x)/((1+x)*(1-2*x)*(1-x)^2).
First differences: a(n+1)-a(n) = A084640(n).
Last digits: a(n) == a(n+10) (mod 10), n>=1.
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MAPLE
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PROG
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(Magma) [(5*2^(n+1)-9-(-1)^n)/6 -2*n: n in [0..40]]; // Vincenzo Librandi, Aug 05 2011
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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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EXTENSIONS
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STATUS
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approved
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