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%I #29 Apr 01 2023 08:48:58
%S 3,4,5,6,8,10,12,17,32,34,40,48,60,85,128,136,160,170,192,204,240,
%T 4369,8192,8224,8704,8738,10240,10280,10880,12288,12336,13056,15360,
%U 15420,16320,65537,131072,131074,131584,139264,139808,163840,164480,174080
%N Numbers k such that sigma(phi(k)) is a prime.
%C Numbers k such that A062402(k) is prime.
%H Michel Marcus, <a href="/A062514/b062514.txt">Table of n, a(n) for n = 1..105</a> (terms 1..73 from Harry J. Smith)
%e Phi(174080)=65536. Sigma(65536) = 131071, a prime.
%o (PARI) je=[]; for(n=1,300000,s=sigma(eulerphi(n)); if(isprime(s),je=concat(je,n))); je
%o (PARI) { n=0; for (m=1, 10^9, if(isprime(sigma(eulerphi(m))), write("b062514.txt", n++, " ", m); if (n==73, break)) ) } \\ _Harry J. Smith_, Aug 08 2009
%Y Cf. A000010, A000203, A062402.
%K easy,nonn
%O 1,1
%A _Jason Earls_, Jul 09 2001