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%I
%S 4,7,13,16,19,25,31,37,43,49,61,64,67,73,79,97,103,109,121,127,139,
%T 151,157,163,169,181,193,199,211,223,229,241,256,271,277,283,289,307,
%U 313,331,337,343,349,361,367,373,379,397,409,421,433,439,457,463,487,499
%N Prime powers congruent to 1 (mod 3).
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CyclotomicGraph.html">Cyclotomic Graph</a>
%t Select[ Range[4, 500], (Mod[#, 3] == 1 && Mod[#, # - EulerPhi[#]] == 0)& ] (* _Jean-François Alcover_, Oct 26 2012 *)
%K nonn,easy
%O 1,1
%A _Eric W. Weisstein_, Feb 12, 2008
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