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%I #19 Jan 17 2019 13:44:07
%S 0,1,4,13,37,46,106,139,469,5695,56281,58669
%N Numbers n such that 8*10^n + 4*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (76*10^n+41)/9 is prime.
%C a(13) > 10^5. - _Robert Price_, Oct 18 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/84449.htm#prime">Prime numbers of the form 844...449</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101069(n-1) + 1 for n>1.
%t Do[ If[ PrimeQ[(76*10^n + 41)/9], Print[n]], {n, 0, 10000}]
%o (PARI) for(n=0, 1e5, if(isprime(k=(76*10^n+41)/9), print1(n", "))) \\ _Altug Alkan_, Oct 19 2015
%Y Cf. A002275, A101069.
%K more,nonn
%O 1,3
%A _Robert G. Wilson v_, Jan 19 2005
%E Inserted a(1)=0 and added a(11)-a(12) by _Robert Price_, Oct 18 2015
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