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A348033
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Number of unitary divisors d of n such that sigma(d)*d is equal to n.
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3
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1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1
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OFFSET
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1
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COMMENTS
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Differs from A327153 for the first time at n=72, where a(72)=0, while A327153(72) = 1.
Conjecture: For all terms x > 1 of A019278, a(x) = 0.
Question: Are there any terms larger than 1?
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LINKS
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FORMULA
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a(n) = Sum_{d|n} [1==gcd(d, n/d) and A000203(d)*d == n], where [ ] is the Iverson bracket.
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MATHEMATICA
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a[n_] := DivisorSum[n, 1 &, CoprimeQ[#, n/#] && #*DivisorSigma[1, #] == n &]; Array[a, 120] (* Amiram Eldar, Sep 27 2021 *)
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PROG
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(PARI) A348033(n) = sumdiv(n, d, if(1==gcd(d, n/d)&&n==(d*sigma(d)), 1, 0));
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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