%I A102947
%S A102947 1,2,3,4,13,14,76,237,872,988,1280,1370,2686,3612,4051,4645,9162
%N A102947 Numbers n such that 2*10^n-3 is prime.
%C A102947 Numbers n such that 10^n + 8*R_n - 2 is prime, where R_n = 11...1 is 
               the repunit (A002275) of length n.
%H A102947 Makoto Kamada, <a href="http://homepage2.nifty.com/m_kamada/math/19997.htm">
               Factorizations of 199...997</a>.
%H A102947 <a href="Sindx_Pri.html#Pri_rep">Index entries for primes involving repunits</
               a>.
%t A102947 Do[ If[ PrimeQ[2*10^n - 3], Print[n]], {n, 0, 10000}]
%Y A102947 Sequence in context: A117342 A123215 A126129 this_sequence A162222 A010346 
               A089142
%Y A102947 Adjacent sequences: A102944 A102945 A102946 this_sequence A102948 A102949 
               A102950
%K A102947 more,nonn
%O A102947 1,2
%A A102947 Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 16 2004