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%I #12 Dec 19 2024 21:16:39
%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 k such that sigma(phi(sigma(k))) = phi(k).
%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) isok(k) = { sigma(eulerphi(sigma(k))) == eulerphi(k) } \\ _Harry J. Smith_, Feb 17 2010
%K nonn
%O 1,2
%A _Joseph L. Pe_, Jan 02 2002