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A270797
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a(n) = J(n) if n odd, or 4*J(n) if n even, where J = Jacobsthal numbers A001045.
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1
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0, 1, 4, 3, 20, 11, 84, 43, 340, 171, 1364, 683, 5460, 2731, 21844, 10923, 87380, 43691, 349524, 174763, 1398100, 699051, 5592404, 2796203, 22369620, 11184811, 89478484, 44739243, 357913940, 178956971, 1431655764, 715827883, 5726623060, 2863311531, 22906492244
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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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a(n) = (-3+3*(-2)^n-5*(-1)^n+5*2^n)/6.
a(n) = (2^(n+3)-8)/6 for n even.
a(n) = (2^(n+1)+2)/6 for n odd.
a(n) = 5*a(n-2)-4*a(n-4) for n>3.
G.f.: x*(1+4*x-2*x^2) / ((1-x)*(1+x)*(1-2*x)*(1+2*x)).
(End)
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PROG
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(PARI) concat(0, Vec(x*(1+4*x-2*x^2)/((1-x)*(1+x)*(1-2*x)*(1+2*x)) + O(x^50))) \\ Colin Barker, Apr 01 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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