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A066930 Numbers n such that phi(sigma(n)) divides sigma(phi(n)). 2

%I

%S 1,7,9,29,71,97,109,121,139,142,175,183,194,215,225,242,244,261,278,

%T 311,344,349,355,430,497,509,516,533,556,571,605,622,631,647,673,709,

%U 729,791,817,859,911,923,1021,1066,1112,1119,1142,1207,1243,1262,1277

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

%H Harry J. Smith, <a href="/A066930/b066930.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[1300],Divisible[DivisorSigma[1,EulerPhi[#]],EulerPhi[ DivisorSigma[ 1,#]]]&] (* _Harvey P. Dale_, Dec 15 2021 *)

%o (PARI) { n=0; for (m=1, 10^10, if (sigma(eulerphi(m)) % eulerphi(sigma(m)) == 0, write("b066930.txt", n++, " ", m); if (n==1000, return)) ) } \\ _Harry J. Smith_, Apr 08 2010

%Y Cf. A033632.

%K nonn

%O 1,2

%A _Benoit Cloitre_, Jan 26 2002

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Last modified August 7 14:56 EDT 2022. Contains 355989 sequences. (Running on oeis4.)