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A190503 Numbers n such that sigma(phi(n)) divides sigma(n). 3


%S 1,2,6,12,14,22,24,28,44,46,48,56,68,87,88,92,94,96,112,118,166,174,

%T 176,184,188,192,214,224,236,332,334,352,358,362,368,376,384,390,410,

%U 428,448,454,472,526,664,668,694,704,716,718,736,752,766,768,856,896

%N Numbers n such that sigma(phi(n)) divides sigma(n).

%C These numbers appear indirectly in A067740, which seeks the least k such that sigma(k)/sigma(phi(k)) = n. Most of these numbers are even. The odd terms (1, 87, 1257, 41559, 56679,...) all appear to produce sigma(n)/sigma(phi(n)) = 1.

%H T. D. Noe, <a href="/A190503/b190503.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[1000], IntegerQ[DivisorSigma[1,#]/DivisorSigma[1,EulerPhi[#]]] &]

%Y Cf. A033631 (n such that sigma(n)/sigma(phi(n)) = 1), A067740.

%Y Cf. A066831 (n such that sigma(n) divides sigma(phi(n))).

%K nonn

%O 1,2

%A _T. D. Noe_, May 11 2011

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Last modified July 4 18:38 EDT 2020. Contains 335448 sequences. (Running on oeis4.)