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A201106
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a(n) = binomial(n^2,3)/(2*n).
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1
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0, 1, 14, 70, 230, 595, 1316, 2604, 4740, 8085, 13090, 20306, 30394, 44135, 62440, 86360, 117096, 156009, 204630, 264670, 338030, 426811, 533324, 660100, 809900, 985725, 1190826, 1428714, 1703170, 2018255, 2378320, 2788016, 3252304, 3776465, 4366110, 5027190
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OFFSET
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1,3
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LINKS
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FORMULA
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a(n) = (n-1)*n*(n^3+n^2-2*n-2)/12.
G.f.: x^2*(1+8*x+x^2) / (x-1)^6. - R. J. Mathar, Nov 28 2011
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MAPLE
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seq(binomial(n^2, 3)/(2*n), n=1..29)
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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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