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A158667
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a(n) = 841*n^2 - 29.
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2
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812, 3335, 7540, 13427, 20996, 30247, 41180, 53795, 68092, 84071, 101732, 121075, 142100, 164807, 189196, 215267, 243020, 272455, 303572, 336371, 370852, 407015, 444860, 484387, 525596, 568487, 613060, 659315, 707252, 756871, 808172, 861155, 915820, 972167, 1030196
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OFFSET
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1,1
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COMMENTS
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The identity (58*n^2-1)^2 - (841*n^2-29)*(2*n)^2 = 1 can be written as A158668(n)^2 - a(n)*A005843(n)^2 = 1.
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LINKS
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FORMULA
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G.f.: 29*x*(-28-31*x+x^2)/(x-1)^3.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).
Sum_{n>=1} 1/a(n) = (1 - cot(Pi/sqrt(29))*Pi/sqrt(29))/58.
Sum_{n>=1} (-1)^(n+1)/a(n) = (cosec(Pi/sqrt(29))*Pi/sqrt(29) - 1)/58. (End)
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MAPLE
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MATHEMATICA
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LinearRecurrence[{3, -3, 1}, {812, 3335, 7540}, 40] (* or *) 29 (29 Range[40]^2 - 1) (* Harvey P. Dale, Oct 31 2011 *)
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PROG
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(Magma) I:=[812, 3335, 7540]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Feb 18 2012
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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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Comment rephrased and redundant formula replaced by R. J. Mathar, Oct 19 2009
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STATUS
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approved
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