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

%S 1,3,6,31,36,61,117,229,339,3165,3958,5277,5343,6079,6535,8485,15084,

%T 34537

%N Numbers n such that 8*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (79*10^n+11)/9 is prime.

%C a(19) > 10^5. - _Robert Price_, Oct 27 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/87779.htm#prime">Prime numbers of the form 877...779</a>.

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

%F a(n) = A101078(n) + 1.

%t Do[ If[ PrimeQ[(79*10^n + 11)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101078.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Jan 19 2005

%E a(17) from Kamada data by _Robert Price_, Dec 14 2010

%E a(18) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013