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A318979
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Number of divisors of n with relatively prime prime indices, meaning they belong to A289509.
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3
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0, 1, 0, 2, 0, 2, 0, 3, 0, 2, 0, 4, 0, 2, 1, 4, 0, 3, 0, 4, 0, 2, 0, 6, 0, 2, 0, 4, 0, 5, 0, 5, 1, 2, 1, 6, 0, 2, 0, 6, 0, 4, 0, 4, 2, 2, 0, 8, 0, 3, 1, 4, 0, 4, 1, 6, 0, 2, 0, 9, 0, 2, 0, 6, 0, 5, 0, 4, 1, 5, 0, 9, 0, 2, 2, 4, 1, 4, 0, 8, 0, 2, 0, 8, 1, 2, 0
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OFFSET
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1,4
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COMMENTS
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A prime index of n is a number m such that prime(m) divides n.
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LINKS
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FORMULA
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EXAMPLE
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The divisors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, 36, corresponding to the prime index multisets (), (1), (2), (11), (12), (22), (112), (122), (1122) respectively. Of these, only (1), (11), (12), (112), (122), (1122) are relatively prime, corresponding to the divisors 2, 4, 6, 12, 18, 36, so a(36) = 6.
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MATHEMATICA
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Table[Length[Select[Divisors[n], GCD@@PrimePi/@FactorInteger[#][[All, 1]]==1&]], {n, 100}]
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PROG
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(PARI) a(n) = sumdiv(n, d, gcd(apply(x->primepi(x), factor(d)[, 1])) == 1); \\ Michel Marcus, Jan 09 2019
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CROSSREFS
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Cf. A000005, A000837, A001221, A018783, A056239, A289508, A289509, A296150, A298748, A318978, A327657.
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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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