%I
%S 1,3,6,51,57,63,150,393,420,547,42024,43063
%N Numbers n such that 10^n + 2*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (11*10^n+61)/9 is prime.
%C a(13) > 10^5.  _Robert Price_, Jan 17 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/1/12229.htm#prime">Prime numbers of the form 122...229</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102011(n) + 1.
%t Do[ If[ PrimeQ[(11*10^n + 61)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A102011.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 16 2004
%E a(11)a(12) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
