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A016161
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Expansion of 1/((1-5x)(1-7x)).
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5
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1, 12, 109, 888, 6841, 51012, 372709, 2687088, 19200241, 136354812, 964249309, 6798573288, 47834153641, 336059778612, 2358521965909, 16540171339488, 115933787267041, 812299450322412, 5689910849522509
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OFFSET
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0,2
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COMMENTS
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Also, this is the number of incongruent integer-edged Heron triangles whose circumdiameter is the product of n distinct primes each of shape 4k + 1. Cf. A003462, A109021. - R. K. Guy, Jan 31 2007
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LINKS
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Table of n, a(n) for n=0..18.
Index entries for linear recurrences with constant coefficients, signature (12,-35).
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FORMULA
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a(n) = (7^(n+1)-5^(n+1))/2 = A081200(n+1). Binomial transform of A080962. - R. J. Mathar, Sep 18 2008
a(n) = 7*a(n-1) + 5^n. - Vincenzo Librandi, Feb 09 2011
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MATHEMATICA
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CoefficientList[Series[1/((1-5x)(1-7x)), {x, 0, 30}], x] (* or *) LinearRecurrence[ {12, -35}, {1, 12}, 30] (* Harvey P. Dale, Nov 16 2021 *)
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PROG
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(PARI) Vec(1/((1-5*x)*(1-7*x))+O(x^99)) \\ Charles R Greathouse IV, Sep 24 2012
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CROSSREFS
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Sequence in context: A011999 A128877 A085797 * A081200 A351161 A016214
Adjacent sequences: A016158 A016159 A016160 * A016162 A016163 A016164
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane
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STATUS
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approved
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