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%I #13 Jan 17 2019 13:44:07
%S 1,4,8,13,16,44,439,608,1201,2725,5210,59389,118216,198529
%N Numbers n such that 5*10^n + 8*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (53*10^n+1)/9 is prime.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/5/58889.htm#prime">Prime numbers of the form 588...889</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101589(n) + 1.
%t Do[ If[ PrimeQ[(53*10^n + 1)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101589.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 18 2005
%E Addition of a(12)-a(14) from Kamada data by _Robert Price_, Dec 12 2010