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%I #18 Mar 30 2012 18:52:14
%S 21,33,57,65,69,77,85,93,129,133,141,145,161,177,185,201,205,209,213,
%T 217,221,237,249,253,265,301,305,309,321,329,341,365,377,381,393,413,
%U 417,437,445,453,469,473,481,485,489,493,497,501,505,517,533,537,545
%N Squarefree semiprimes of the form 4k+1.
%C There are 961 squarefree semiprimes of the form 4k+1 below 10000.
%H T. D. Noe, <a href="/A190299/b190299.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>
%t Select[Range[1,600,4],Last/@FactorInteger[#]=={1,1}&]
%Y Cf. A001358, A006881, A080774. Union of A131574 and A016105.
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, May 07 2011
%E Edited by _Ray Chandler_, Dec 16 2011
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