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A016161
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Expansion of g.f. 1/((1-5*x)*(1-7*x)).
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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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FORMULA
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a(n) = (7^(n+1)-5^(n+1))/2 = A081200(n+1).
Binomial transform of A080962. (End)
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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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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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