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%I #20 Jan 17 2019 13:44:07
%S 0,2,3,5,8,14,77,195,218,957,1052,1163,1485,1731,1970,3237,17354,85964
%N Numbers n such that 3*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (32*10^n+31)/9 is prime.
%C a(19) > 10^5. - _Robert Price_, May 31 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/35559.htm#prime">Prime numbers of the form 355...559</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101838(n-1) + 1.
%t Do[ If[ PrimeQ[(32*10^n+31)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101838.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 17 2004
%E Addition of a(17) from Kamada data by _Robert Price_, Dec 12 2010
%E a(18) from _Robert Price_, May 31 2015