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A318734
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a(n) = Sum_{k=1..n} (-1)^(k + 1) * d(2*k - 1), where d(k) is the number of divisors of k (A000005).
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5
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1, -1, 1, -1, 2, 0, 2, -2, 0, -2, 2, 0, 3, -1, 1, -1, 3, -1, 1, -3, -1, -3, 3, 1, 4, 0, 2, -2, 2, 0, 2, -4, 0, -2, 2, 0, 2, -4, 0, -2, 3, 1, 5, 1, 3, -1, 3, -1, 1, -5, -3, -5, 3, 1, 3, -1, 1, -3, 3, -1, 2, -2, 2, 0, 4, 2, 6, -2, 0, -2, 2, -2
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OFFSET
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1,5
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LINKS
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MATHEMATICA
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a[n_] := Sum[(-1)^(k + 1) DivisorSigma[0, 2 k - 1], {k, 1, n}];
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PROG
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(PARI) s=0; j=-1; forstep(k=1, 141, 2, j=-j; s=s+j*numdiv(k); print1(s, ", "))
(PARI) a(n) = sum(k=1, n, (-1)^(k+1)*numdiv(2*k-1)); \\ Michel Marcus, Sep 08 2018
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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