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A166521
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a(n) = (6*n + 7*(-1)^n + 3)/2.
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1
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1, 11, 7, 17, 13, 23, 19, 29, 25, 35, 31, 41, 37, 47, 43, 53, 49, 59, 55, 65, 61, 71, 67, 77, 73, 83, 79, 89, 85, 95, 91, 101, 97, 107, 103, 113, 109, 119, 115, 125, 121, 131, 127, 137, 133, 143, 139, 149, 145, 155, 151, 161, 157, 167, 163, 173, 169, 179, 175, 185
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = 6*n - a(n-1), with n>1, a(1)=1.
G.f.: -x*(-1-10*x+5*x^2) / ((1+x)*(x-1)^2). - R. J. Mathar, Mar 08 2011
E.g.f.: (1/2)*(7*exp(-x) + 3*(1+2*x)*exp(x) -10).
a(n) = a(n-1) + a(n-2) - a(n-3). (End)
Sum_{n>=1} (-1)^(n+1)/a(n) = 1/5 + Pi/(2*sqrt(3)). - Amiram Eldar, Feb 24 2023
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MATHEMATICA
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LinearRecurrence[{1, 1, -1}, {1, 11, 7}, 90] (* Harvey P. Dale, Apr 29 2018 *)
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PROG
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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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