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A129362
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a(n) = Sum_{k=floor((n+1)/2)..n} J(k+1), J(k) = A001045(k).
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3
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1, 1, 4, 8, 19, 37, 80, 160, 331, 661, 1344, 2688, 5419, 10837, 21760, 43520, 87211, 174421, 349184, 698368, 1397419, 2794837, 5591040, 11182080, 22366891, 44733781, 89473024, 178946048, 357903019, 715806037
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OFFSET
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0,3
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LINKS
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FORMULA
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G.f.: (1+2*x^3)/((1-x-2*x^2)*(1-x^2-2*x^4)).
a(n) = a(n-1) + 3*a(n-2) - a(n-3) - 2*a(n-5) - 4*a(n-6).
a(n) = Sum_{k=0..n} ( J(k+1) - J((k+1)/2)*(1-(-1)^k)/2 ).
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MATHEMATICA
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LinearRecurrence[{1, 3, -1, 0, -2, -4}, {1, 1, 4, 8, 19, 37}, 30] (* Harvey P. Dale, Oct 22 2011 *)
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PROG
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(Magma)
A001045:= func< n | (2^n - (-1)^n)/3 >;
(SageMath)
def A001045(n): return (2^n - (-1)^n)/3
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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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