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%I #17 Nov 21 2013 13:07:15
%S 15,35,39,51,55,87,91,95,111,115,119,123,143,155,159,183,187,203,215,
%T 219,235,247,259,267,287,291,295,299,303,319,323,327,335,339,355,371,
%U 391,395,403,407,411,415,427,447,451,471,511,515,519,527,535,543,551
%N Numbers with two prime factors: (4*i+1)*(4*j+3).
%C Semiprimes of the form 4k+3. - _Giovanni Teofilatto_, Jun 15 2005
%C There are 971 semiprimes of the form 4k+3 below 10,000.
%H T. D. Noe, <a href="/A080774/b080774.txt">Table of n, a(n) for n=1..1000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Semiprime.html">Semiprime</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Semiprime">Semiprime</a>
%e a(1) = 15 = 3*5 = (4*1+1)*(4*0+3).
%t Select[Range[15, 1000, 2], Last /@ FactorInteger[#] == {1, 1} && IntegerQ[(# - 3)/4] &] (* _Vladimir Joseph Stephan Orlovsky_, May 07 2011 *)
%Y Cf. A001358, A006881, A002144, A002145, A107978, A121387.
%K nonn
%O 1,1
%A _Reinhard Zumkeller_, Mar 10 2003
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