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A067931
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Numbers k that divide the alternating sum sigma(1) - sigma(2) + sigma(3) - sigma(4) + ... + ((-1)^(k+1))*sigma(k).
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2
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1, 2, 11, 19, 36, 45, 152, 377, 418, 3794, 4423, 14495, 31148, 42224, 49279, 120447, 1018376, 2605261, 17484247, 368070997, 850833878, 1121254607, 3440701629, 7863041200
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OFFSET
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1,2
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COMMENTS
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No further term below 10^7.
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LINKS
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EXAMPLE
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sigma(1) - sigma(2) = -2, which is divisible by 2, so 2 is a term of the sequence.
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MATHEMATICA
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s = 0; Do[s = s + (-1)^(i + 1) * DivisorSigma[1, i]; If[Mod[s, i] == 0, Print[i]], {i, 1, 10^5}]
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PROG
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(PARI) {a067931(m)=local(s, n); s=0; for(n=1, m, if(n%2==0, s=s-sigma(n), s=s+sigma(n)); if(s%n==0, print1(n, ", ")))}
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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