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%I #14 Jan 17 2019 13:44:07
%S 0,3,143,797,3143,18791,20763,96743
%N Numbers n such that 3*10^n + R_n + 8 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (28*10^n+71)/9 is prime.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/31119.htm#prime">Prime numbers of the form 311...119</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101827(n-1) + 1.
%t Do[ If[ PrimeQ[(28*10^n+71)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101827.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 17 2004
%E Two more PRP terms from _Serge Batalov_, Nov 17 2008
%E Addition of a(8) from Kamada data by _Robert Price_, Dec 13 2010