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A109020
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(2*7^n - 3*3^n + 1)/6.
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1
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0, 1, 12, 101, 760, 5481, 38852, 273421, 1918320, 13441361, 94128892, 659020341, 4613496680, 32295539641, 226071966132, 1582513328861, 11077621999840, 77543440092321, 542804338926572, 3799631147326981, 26597420355811800, 186181949464251401, 1303273667170466212
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OFFSET
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0,3
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COMMENTS
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Number of incongruent integer-edged Heron triangles whose circumdiameter is the product of n distinct primes of shape 4k + 1.
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LINKS
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FORMULA
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a(0)=0, a(1)=1, a(2)=12, a(n)=11*a(n-1)-31*a(n-2)+21*a(n-3) -- From Harvey P. Dale, Aug 10 2012
G.f.: (-x^2-x)/(21*x^3-31*x^2+11*x-1) -- From Harvey P. Dale, Aug 10 2012
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MATHEMATICA
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Table[(2*7^n-3*3^n+1)/6, {n, 0, 30}] (* or *) LinearRecurrence[{11, -31, 21}, {0, 1, 12}, 30] (* Harvey P. Dale, Aug 10 2012 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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