A066465 - OEIS

%I #9 Jan 03 2017 02:17:12

%S 1,13,43,97,211,533,1133,2627,3907,4687,4801,11231,15689,33613,45995,

%T 82643,92543,106571,143903,156383,159947,173239,190399,370913,390247,

%U 393049,437747,487547,513193,519601,577633,616399,715163,740213,883387

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

%H Harry J. Smith, <a href="/A066465/b066465.txt">Table of n, a(n) for n = 1..650</a>

%t Select[Range[1, 10^6], DivisorSigma[1, EulerPhi[DivisorSigma[1, # ]]] == EulerPhi[ # ] &]

%o (PARI) { n=0; for (m=1, 10^10, if (sigma(eulerphi(sigma(m))) == eulerphi(m), write("b066465.txt", n++, " ", m); if (n==1000, return)) ) } \\ _Harry J. Smith_, Feb 17 2010

%K nonn

%O 1,2

%A _Joseph L. Pe_, Jan 02 2002