%I #19 Jan 17 2019 13:44:07

%S 1,2,7,44,56,338,1211,2693,3536,3917,3974,4046,6961,23771,69656

%N Numbers n such that 8*10^n + 5*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (77*10^n-23)/9 is prime.

%C a(16) > 10^5. - _Robert Price_, Oct 22 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/85553.htm#prime">Prime numbers of the form 855...553</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%F a(n) = A101071(n) + 1.

%t Do[ If[ PrimeQ[(77*10^n - 23)/9], Print[n]], {n, 0, 10000}]

%o (PARI) for(n=0, 1e5, if(isprime((77*10^n-23)/9), print1(n, ", "))) \\ _Altug Alkan_, Oct 22 2015

%Y Cf. A002275, A101071.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Jan 19 2005

%E a(14) from Kamada data by _Robert Price_, Dec 14 2010

%E a(15) from _Robert Price_, Oct 22 2015