DivisorSigma[1, n] == DivisorSum[DivisorSigma[0, n/Subscript[d, j]] EulerPhi[Subscript[d, j]], {Subscript[d, j], n}] /; Element[Subscript[d, j], Divisors[n]] && Element[n, Integers] && n > 0

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2007-05-02