%I
%S 2,4,26,1271,1412,3328,4676,47051,67664
%N Numbers n such that 4*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 (43*10^n+11)/9 is prime.
%C a(10) > 10^5.  _Robert Price_, Jun 01 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/47779.htm#prime">Prime numbers of the form 477...779</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101733(n) + 1.
%t Do[ If[ PrimeQ[(43*10^n + 11)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101733.
%K more,nonn
%O 1,1
%A _Robert G. Wilson v_, Jan 17 2005
%E a(8) from Erik Branger, May 01 2013, submitted by _Ray Chandler_, Aug 16 2013
%E a(9) from _Robert Price_, Jun 01 2015
