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A284446
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a(n) = Sum_{d|n, d == 5 (mod 7)} d.
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10
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0, 0, 0, 0, 5, 0, 0, 0, 0, 5, 0, 12, 0, 0, 5, 0, 0, 0, 19, 5, 0, 0, 0, 12, 5, 26, 0, 0, 0, 5, 0, 0, 33, 0, 5, 12, 0, 19, 0, 45, 0, 0, 0, 0, 5, 0, 47, 12, 0, 5, 0, 26, 0, 54, 5, 0, 19, 0, 0, 17, 61, 0, 0, 0, 5, 33, 0, 68, 0, 5, 0, 12, 0, 0, 80, 19, 0, 26, 0, 45, 0, 82
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OFFSET
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1,5
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LINKS
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FORMULA
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G.f.: Sum_{k>=0} (5+7k) x^(5+7k)/(1-x^(5+7k)). - Robert Israel, Mar 27 2017
Sum_{k=1..n} a(k) = c * n^2 + O(n*log(n)), where c = Pi^2/84 = 0.117495... . - Amiram Eldar, Nov 26 2023
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MAPLE
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f:= n -> convert(select(t -> t mod 7 = 5, numtheory:-divisors(n)), `+`):
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MATHEMATICA
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Table[DivisorSum[n, # &, Mod[#, 7] == 5 &], {n, 82}] (* Giovanni Resta, Mar 27 2017 *)
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PROG
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(PARI) for(n=1, 82, print1(sumdiv(n, d, if(Mod(d, 7)==5, d, 0)), ", ")) \\ Indranil Ghosh, Mar 27 2017
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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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