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A062113
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a(0)=1; a(1)=2; a(n) = a(n-1) + a(n-2)*(3 - (-1)^n)/2.
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2
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1, 2, 3, 7, 10, 24, 34, 82, 116, 280, 396, 956, 1352, 3264, 4616, 11144, 15760, 38048, 53808, 129904, 183712, 443520, 627232, 1514272, 2141504, 5170048, 7311552, 17651648, 24963200, 60266496, 85229696, 205762688, 290992384, 702517760
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OFFSET
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0,2
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COMMENTS
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A bistable recurrence.
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LINKS
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FORMULA
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a(n) = 4*a(n-2) - 2*a(n-4).
G.f.: (1+2*x-x^2-x^3)/(1-4*x^2+2*x^4). (End)
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MATHEMATICA
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LinearRecurrence[{0, 4, 0, -2}, {1, 2, 3, 7}, 40] (* G. C. Greubel, Oct 16 2018 *)
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PROG
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(PARI) { for (n=0, 200, if (n>1, a=a1 + a2*(3 - (-1)^n)/2; a2=a1; a1=a, if (n==0, a=a2=1, a=a1=2)); write("b062113.txt", n, " ", a) ) } \\ Harry J. Smith, Aug 01 2009
(PARI) x='x+O('x^40); Vec((1+2*x-x^2-x^3)/(1-4*x^2+2*x^4)) \\ G. C. Greubel, Oct 16 2018
(Haskell)
a062113 n = a062113_list !! n
a062113_list = 1 : 2 : zipWith (+)
(tail a062113_list) (zipWith (*) a000034_list a062113_list)
(Magma) I:=[1, 2, 3, 7]; [n le 4 select I[n] else 4*Self(n-2) - 2*Self(n-4): n in [1..40]]; // G. C. Greubel, Oct 16 2018
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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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STATUS
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approved
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