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A279926
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a(n) = Sum_{k=1..n-1} sigma_3(k)*sigma_9(n-k).
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1
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0, 1, 522, 24329, 454250, 4905766, 36532244, 207705929, 961214238, 3784166376, 13066960126, 40511160326, 114681233758, 300599979884, 737035375772, 1705830324553, 3751239987240, 7887626314003, 15927815870322, 31031953887704, 58508991327728, 107133058597170
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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) = (sigma_13(n) - 11*sigma_9(n) + 10*sigma_3(n))/2640.
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MATHEMATICA
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Table[Sum[If[k == 0, 0, DivisorSigma[3, k]] DivisorSigma[9, n - k], {k, 0, n - 1}], {n, 22}] (* Michael De Vlieger, Dec 23 2016 *)
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PROG
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(PARI) a(n) = sum(k=1, n-1, sigma(k, 3)*sigma(n-k, 9)) \\ Felix Fröhlich, Dec 23 2016
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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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