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A091286 Numbers n such that Sigma[3,n] is divisible by square of cototient of n, while n is not a prime number. +0
1
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 (list; graph; listen)
OFFSET

1,1

EXAMPLE

n=15: cototient[15]=7,sigma[3,15]=3528=72.49

MATHEMATICA

Do[s=DivisorSigma[3, n]/(n-EulerPhi[n])^2; If[IntegerQ[s]&&!PrimeQ[n], Print[n]], {n, 1, 100000}]

CROSSREFS

Cf. A091285.

Sequence in context: A050405 A020136 A067401 this_sequence A064058 A138322 A010822

Adjacent sequences: A091283 A091284 A091285 this_sequence A091287 A091288 A091289

KEYWORD

nonn

AUTHOR

Labos E. (labos(AT)ana.sote.hu), Feb 03 2004

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Last modified July 25 07:41 EDT 2008. Contains 142293 sequences.


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