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A091286
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Numbers n such that sigma_3(n) is divisible by square of cototient of n, while n is not a prime number.
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1
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15, 85, 259, 295, 391, 589, 799, 1111, 1717, 3193, 4171, 4369, 12361, 17473, 23533, 25429, 28243, 31351, 34477, 36181, 41407, 47989, 51143, 52537, 58103, 65641, 68377, 69541, 69919, 70453, 72619, 81121, 83131, 83767, 85069, 91759
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OFFSET
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1,1
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LINKS
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EXAMPLE
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n=15: cototient(15) = 7, sigma_3(15) = 3528 = 72 * 49.
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MATHEMATICA
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Do[s=DivisorSigma[3, n]/(n-EulerPhi[n])^2; If[IntegerQ[s]&&!PrimeQ[n], Print[n]], {n, 1, 100000}]
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PROG
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(PARI) isok(n) = (n!=1) && !isprime(n) && !(sigma(n, 3)%(n-eulerphi(n))^2); \\ Michel Marcus, Aug 13 2019
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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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