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%I #7 Mar 31 2012 10:27:23
%S 2,7,25,115,670,4324,30657,229568,1775675,14156112,115500275,960392564
%N Number of safe primes < 10^n.
%C Number of safe primes with at most n digits; or a(10^n).
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Safe_prime">Safe prime</a>
%e a(10^2) = a(100) = #{5, 7, 11, 23, 47, 59, 83} = 7
%Y A156875, A006880, A005385
%K nonn
%O 1,1
%A _Krzysztof Ostrowski_, Apr 09 2011