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A279964
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a(n) = Sum_{k=1..n-1} sigma_3(k)*sigma_7(n-k).
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3
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0, 1, 138, 3377, 39890, 297550, 1623980, 7065329, 25808790, 82305816, 234756742, 611706830, 1474831246, 3334313204, 7118797268, 14485772017, 28206850488, 52921773667, 95877425634, 168644231672, 288301373792, 481166453010, 784226941604, 1253068878542, 1962356045590
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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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36*tau(n) = 5*sigma_3(n) + 10*sigma_7(n) + 21*sigma_5(n) + 2400*a(n) - 5292*A279889(n).
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MATHEMATICA
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Table[Sum[DivisorSigma[3, k] * DivisorSigma[7, n - k], {k, 1, n - 1}], {n, 1, 25}] (* Indranil Ghosh, Mar 12 2017 *)
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PROG
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(PARI) a(n) = sum(k=1, n-1, sigma(k, 3)*sigma(n-k, 7)); \\ Michel Marcus, Dec 24 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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