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A088941
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a(n)=12*sum(1<=i<=j<=k<=n,i*j/k).
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4
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0, 12, 54, 154, 349, 685, 1217, 2009, 3134, 4674, 6720, 9372, 12739, 16939, 22099, 28355, 35852, 44744, 55194, 67374, 81465, 97657, 116149, 137149, 160874, 187550, 217412, 250704, 287679, 328599, 373735, 423367, 477784, 537284, 602174, 672770
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OFFSET
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0,2
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COMMENTS
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Always an integer.
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LINKS
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FORMULA
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a(n)=(n/24)*(9*n^3 + 58*n^2 + 123*n + 98).
G.f.: x*(x^3-4*x^2+6*x-12) / (x-1)^5. - Colin Barker, Jun 15 2013
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MATHEMATICA
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LinearRecurrence[{5, -10, 10, -5, 1}, {0, 12, 54, 154, 349}, 40] (* Harvey P. Dale, May 01 2014 *)
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PROG
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(PARI) a(n)=if(n<0, 0, a(n)=n/24*(9*n^3 + 58*n^2 + 123*n + 98))
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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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