%I #22 Jan 17 2019 13:44:07
%S 1,4,136,181,325,3292,3871,4690,7876,11911,16096,21649,43045
%N Numbers n such that 4*10^n + 2*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (38*10^n+43)/9 is prime.
%C a(14) > 10^5. - _Robert Price_, May 08 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/42227.htm#prime">Prime numbers of the form 422...227</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101721(n) + 1.
%t Do[ If[ PrimeQ[(38*10^n + 43)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101721.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 17 2005
%E Addition of a(10)-a(12) from Kamada data by _Robert Price_, Dec 13 2010
%E a(13) from Erik Branger, May 01 2013, submitted by _Ray Chandler_, Aug 16 2013
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