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A066463 Numbers n such that phi(sigma(phi(n))) = phi(n). 1

%I

%S 1,2,3,4,6,13,15,16,20,21,24,26,28,30,36,42,241,255,256,272,287,305,

%T 320,325,340,369,384,385,408,429,465,480,482,488,495,496,510,525,572,

%U 574,610,616,620,650,700,732,738,744,770,779,792,793,803,858,900,905

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

%H Harry J. Smith, <a href="/A066463/b066463.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[1, 10^3], EulerPhi[DivisorSigma[1, EulerPhi[ # ]]] == EulerPhi[ # ] &]

%o (PARI) { n=0; for (m=1, 10^10, if (eulerphi(sigma(eulerphi(m))) == eulerphi(m), write("b066463.txt", n++, " ", m); if (n==1000, return)) ) } \\ _Harry J. Smith_, Feb 16 2010

%K nonn

%O 1,2

%A _Joseph L. Pe_, Jan 02 2002

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Last modified July 28 11:11 EDT 2021. Contains 346326 sequences. (Running on oeis4.)