%I #10 Nov 20 2014 09:28:56

%S 10,34,57,74,85,185,202,219,394,451,489,505,514,629,679,802,985,1057,

%T 1154,1285,1354,1387,1417,1717,2005,2047,2509,2594,2649,2761,2885,

%U 3097,3202,3277,3349,3385,3409,3459,3737,4207,4369,4377,4577

%N Semiprimes n such that phi(n) is a square.

%C Freiberg & Pomerance show that this sequence is infinite and a(n) << n^2 log^2 n.

%H Charles R Greathouse IV, <a href="/A247129/b247129.txt">Table of n, a(n) for n = 1..10000</a>

%H Tristan Freiberg, Carl Pomerance, <a href="http://arxiv.org/abs/1410.8109">A note on square totients</a>, arXiv:1410.8109 [math.NT], 2014.

%o (PARI) is(n)=issquare(eulerphi(n))&&bigomega(n)==2

%o (PARI) list(lim)=my(v=List()); forprime(p=2,sqrtint(lim\1), forprime(q=p+1, lim\p, if(issquare((p-1)*(q-1)), listput(v,p*q)))); Set(v)

%Y Cf. A039770, A221285, A002496.

%K nonn

%O 1,1

%A _Charles R Greathouse IV_, Nov 19 2014