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%I #2 Oct 02 2013 15:47:26
%S 57,77,3777,17777,277777,1777777,17777777,707777777,3777777777,
%T 17777777777,577777777777,1777777777777,37777777777777,
%U 757777777777777,4777777777777777,37777777777777777,277777777777777777
%N Smallest semiprime containing exactly n 7's.
%e a(2)=77 because 77 is the smallest semiprime containing exactly two 7's.
%K base,nonn
%O 1,1
%A _Shyam Sunder Gupta_, Apr 24 2005