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%I #21 Jan 17 2019 13:44:07
%S 0,2,3,5,6,20,776,1185,3164,4212,10733,21726,38235
%N Numbers n such that 3*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 (34*10^n+11)/9 is prime.
%C a(14) > 10^5. - _Robert Price_, May 08 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/37779.htm#prime">Prime numbers of the form 377...779</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101843(n-1) + 1.
%t Do[ If[ PrimeQ[(34*10^n + 11)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101843.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 17 2004
%E Addition of a(11)-a(12) from Kamada data by _Robert Price_, Dec 13 2010
%E a(13) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
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