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A122255
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Characteristic function of numbers with 3-smooth Euler's totient (A000010).
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6
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1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Multiplicative with a(p^e) = 1 for e = 1 and A006530(p-1) <= 3 or p <= 3; otherwise 0. - Andrew Howroyd, Aug 01 2018
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EXAMPLE
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For n = 25, phi(25) = 20 = 2^2 * 5^1, and this is not 3-smooth, thus a(25) = 0.
For n = 26, phi(26) = 12 = 2^4 * 3^1, and here there are no larger prime factors than 3 (12 is 3-smooth), thus a(26) = 1. - Antti Karttunen, Aug 22 2017
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MATHEMATICA
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a[n_] := Boole[FactorInteger[EulerPhi[n]][[-1, 1]] <= 3];
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PROG
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CROSSREFS
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Characteristic function of A122254.
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KEYWORD
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nonn,mult
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AUTHOR
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STATUS
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approved
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