%I
%S 21,33,57,65,69,77,85,93,125,129,133,141,145,161,177,185,201,205,209,
%T 213,217,221,237,249,253,265,301,305,309,321,329,341,365,377,381,393,
%U 413,417,437,445,453,469,473,481,485,489,493,497,501,505,517,533,537,545
%N Numbers of the form 4k+1 having exactly 4 divisors.
%C Intersection of A016813 and A030513; subsequence of A007422.
%C Numbers p*q with p = q (mod 4) together with p^3 with p=1 (mod 4), p and q distinct primes.  _Charles R Greathouse IV_, May 03 2011
%H G. C. Greubel, <a href="/A189986/b189986.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[4Range[200]+1,DivisorSigma[0,#]==4&] (* _Harvey P. Dale_, May 11 2011 *)
%o (MAGMA) [ n: n in [1..600 by 4]  #Divisors(n) eq 4 ]; // _Klaus Brockhaus_, May 04 2011
%Y Cf. A007422, A016813, A030513.
%K nonn
%O 1,1
%A _JuriStepan Gerasimov_, May 03 2011
%E Corrected (497 inserted) by _Klaus Brockhaus_, May 04 2011
