%I A056701
%S A056701 0,1,2,3,4,10,16,22,53,91,94,106,138,210,282,522,597,1049,2227,6459,
%T A056701 10582
%N A056701 Numbers n such that 2*10^n + 3*R_n is prime, where R_n = 11...1 is the 
               repunit (A002275) of length n.
%C A056701 Also numbers n such that (7*10^n-1)/3 is prime.
%H A056701 Makoto Kamada, <a href="http://homepage2.nifty.com/m_kamada/math/23333.htm">
               Factorizations of 233...33</a>
%H A056701 <a href="Sindx_Pri.html#Pri_rep">Index entries for primes involving repunits</
               a>
%t A056701 Do[ If[ PrimeQ[ 2*10^n + 3*(10^n-1)/9], Print[n]], {n, 0, 15001}]
%Y A056701 Sequence in context: A095384 A115899 A085934 this_sequence A055506 A098088 
               A080500
%Y A056701 Adjacent sequences: A056698 A056699 A056700 this_sequence A056702 A056703 
               A056704
%K A056701 hard,nonn
%O A056701 1,3
%A A056701 Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000