%I #16 Jan 17 2019 13:44:07
%S 1,2,8,17,19,25,40,49,58,59,92,113,296,637,1856,2515,3593,6991,11840,
%T 86072,93508
%N Numbers n such that 8*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 (77*10^n+31)/9 is prime.
%C a(22) > 10^5. - _Robert Price_, Oct 26 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/85559.htm#prime">Prime numbers of the form 855...559</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101073(n) + 1.
%t Do[ If[ PrimeQ[(77*10^n + 31)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101073.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 19 2005
%E a(19) from Kamada data by _Robert Price_, Dec 14 2010
%E a(20)-a(21) from _Robert Price_, Oct 26 2015