%I A066850
%S A066850 1,4,2669,9559,15293,32583,36593,38443,255367,257239,273977,283391,
%T A066850 314101,421553,488363,532975,768699,839973,871757,1960479,2337221,
%U A066850 2374867,3084659,3326653,3735029,4440017,5387373,7930439,8114377
%N A066850 Numbers n such that phi(phi(n)) + sigma(sigma(n)) = phi(sigma(n)) + sigma(phi(n)), 
               where phi=A000010 is Euler's totient function and sigma=A000203 is 
               the sum of divisors function.
%e A066850 Let n = 2669. Then phi(phi(n)) + sigma(sigma(n)) = phi(2496) + sigma(2844) 
               = 768 + 7280 = 8048 and phi(sigma(n)) + sigma(phi(n)) = phi(2844) 
               + sigma(2496) = 936 + 7112 = 8048. So 2669 is in the sequence.
%t A066850 g[x_] := Module[{a, b, c, d, e, f}, a = EulerPhi[x]; b = DivisorSigma[1, 
               x]; c = EulerPhi[a]; d = DivisorSigma[1, b]; e = EulerPhi[b]; f = 
               DivisorSigma[1, a]; c + d - e - f]; Do[If[g[n] == 0, Print[n]], {n, 
               1, 10^6}]
%Y A066850 Sequence in context: A047676 A079187 A131587 this_sequence A066837 A132639 
               A132643
%Y A066850 Adjacent sequences: A066847 A066848 A066849 this_sequence A066851 A066852 
               A066853
%K A066850 nonn
%O A066850 1,2
%A A066850 Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 24 2002
%E A066850 Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Jan 24 2002