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A363803
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a(n) = Sum_{d|n, d == 0, 2, or 5 mod 7} d.
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2
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0, 2, 0, 2, 5, 2, 7, 2, 9, 7, 0, 14, 0, 23, 5, 18, 0, 11, 19, 7, 28, 2, 23, 14, 5, 28, 9, 51, 0, 37, 0, 18, 33, 2, 47, 23, 37, 21, 0, 47, 0, 86, 0, 46, 14, 25, 47, 30, 56, 7, 51, 28, 0, 65, 5, 107, 19, 60, 0, 49, 61, 2, 100, 18, 70, 35, 0, 70, 23, 133, 0, 95, 0, 39, 80, 21, 84, 28, 79, 63, 9, 84, 0
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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, k == 0, 2 or 5 mod 7} k * x^k/(1 - x^k).
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MATHEMATICA
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a[n_] := DivisorSum[n, # &, MemberQ[{0, 2, 5}, Mod[#, 7]] &]; Array[a, 100] (* Amiram Eldar, Jun 23 2023 *)
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PROG
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(PARI) my(N=90, x='x+O('x^N)); concat(0, Vec(sum(k=1, N, [1, 0, 1, 0, 0, 1, 0][k%7+1]*k*x^k/(1-x^k))))
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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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