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A318874
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Number of divisors d of n for which 2*phi(d) > d.
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5
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1, 1, 2, 1, 2, 2, 2, 1, 3, 2, 2, 2, 2, 2, 4, 1, 2, 3, 2, 2, 4, 2, 2, 2, 3, 2, 4, 2, 2, 4, 2, 1, 4, 2, 4, 3, 2, 2, 4, 2, 2, 4, 2, 2, 6, 2, 2, 2, 3, 3, 4, 2, 2, 4, 4, 2, 4, 2, 2, 4, 2, 2, 6, 1, 4, 4, 2, 2, 4, 4, 2, 3, 2, 2, 6, 2, 4, 4, 2, 2, 5, 2, 2, 4, 4, 2, 4, 2, 2, 6, 4, 2, 4, 2, 4, 2, 2, 3, 6, 3, 2, 4, 2, 2, 7
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OFFSET
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1,3
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LINKS
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FORMULA
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EXAMPLE
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n = 105 has eight divisors: [1, 3, 5, 7, 15, 21, 35, 105]. When A083254 is applied to them, we obtain [1, 1, 3, 5, 1, 3, 13, -9], and seven of these numbers are positive, thus a(105) = 7.
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MAPLE
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A318874 := n -> nops(select(d -> (2*numtheory:-phi(d)) > d, divisors(n))):
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MATHEMATICA
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A318874[n_] := DivisorSum[n, 1 &, 2*EulerPhi[#] > # &];
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PROG
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(PARI) A318874(n) = sumdiv(n, d, (2*eulerphi(d))>d);
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CROSSREFS
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Differs from A001227 for the first time at n=105, where a(105) = 7, while A001227(105) = 8.
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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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