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 A016161 Expansion of 1/((1-5x)(1-7x)). 5
 1, 12, 109, 888, 6841, 51012, 372709, 2687088, 19200241, 136354812, 964249309, 6798573288, 47834153641, 336059778612, 2358521965909, 16540171339488, 115933787267041, 812299450322412, 5689910849522509 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS 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 LINKS Index entries for linear recurrences with constant coefficients, signature (12,-35). FORMULA 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 MATHEMATICA CoefficientList[Series[1/((1-5x)(1-7x)), {x, 0, 30}], x] (* or *) LinearRecurrence[ {12, -35}, {1, 12}, 30] (* Harvey P. Dale, Nov 16 2021 *) PROG (PARI) Vec(1/((1-5*x)*(1-7*x))+O(x^99)) \\ Charles R Greathouse IV, Sep 24 2012 CROSSREFS Sequence in context: A011999 A128877 A085797 * A081200 A016214 A037581 Adjacent sequences:  A016158 A016159 A016160 * A016162 A016163 A016164 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified January 26 23:54 EST 2022. Contains 350601 sequences. (Running on oeis4.)