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A284280
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a(n) = Sum_{d|n, d == 2 (mod 5)} d.
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12
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0, 2, 0, 2, 0, 2, 7, 2, 0, 2, 0, 14, 0, 9, 0, 2, 17, 2, 0, 2, 7, 24, 0, 14, 0, 2, 27, 9, 0, 2, 0, 34, 0, 19, 7, 14, 37, 2, 0, 2, 0, 51, 0, 24, 0, 2, 47, 14, 7, 2, 17, 54, 0, 29, 0, 9, 57, 2, 0, 14, 0, 64, 7, 34, 0, 24, 67, 19, 0, 9, 0, 86, 0, 39, 0, 2, 84, 2, 0, 2
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OFFSET
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1,2
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LINKS
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FORMULA
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G.f.: Sum_{k>=0} (5*k + 2)*x^(5*k+2)/(1 - x^(5*k+2)). - Ilya Gutkovskiy, Mar 25 2017
Sum_{k=1..n} a(k) = c * n^2 + O(n*log(n)), where c = Pi^2/60 = 0.164493... (A013661 / 10). - Amiram Eldar, Nov 26 2023
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MATHEMATICA
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Table[Sum[If[Mod[d, 5] == 2, d, 0], {d, Divisors[n]}], {n, 80}] (* Indranil Ghosh, Mar 24 2017 *)
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PROG
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(PARI) for(n=1, 80, print1(sumdiv(n, d, if(Mod(d, 5)==2, d, 0)), ", ")) \\ Indranil Ghosh, Mar 24 2017
(Python)
from sympy import divisors
def a(n): return sum([d for d in divisors(n) if d%5==2]) # Indranil Ghosh, Mar 24 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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