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13, 39, 79, 133, 201, 283, 379, 489, 613, 751, 903, 1069, 1249, 1443, 1651, 1873, 2109, 2359, 2623, 2901, 3193, 3499, 3819, 4153, 4501, 4863, 5239, 5629, 6033, 6451, 6883, 7329, 7789, 8263, 8751, 9253, 9769, 10299, 10843, 11401, 11973, 12559, 13159, 13773
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OFFSET
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1,1
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COMMENTS
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Consider the quadratic cyclotomic polynomial f(x) = x^2+x+1 and the quotients defined by f(x + n*f(x))/f(x). a(n) is the quotient at x=2.
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LINKS
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FORMULA
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a(1)=13, a(2)=39, a(3)=79, a(n)=3*a(n-1)-3*a(n-2)+a(n-3). - Harvey P. Dale, Feb 07 2015
G.f.: (1 + 10*x + 3*x^2)/(1-x)^3.
E.g.f.: (1 + 12*x + 7*x^2)*exp(x). (End)
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EXAMPLE
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When x = 2, f(x) = 7. Hence at n=1, f( x + f(x))/f(x) = 13 = a(1).
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MATHEMATICA
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Table[1+5n+7n^2, {n, 60}] (* or *) LinearRecurrence[{3, -3, 1}, {13, 39, 79}, 60] (* Harvey P. Dale, Feb 07 2015 *)
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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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EXTENSIONS
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Edited, definition simplified, sequence extended beyond a(8) by R. J. Mathar, Nov 23 2009
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STATUS
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approved
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