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%I #22 Jan 17 2019 13:44:07
%S 1,2,4,5,13,22,25,28,38,67,142,284,295,380,397,1217,1640,2885,3286,
%T 7735,29306
%N Numbers n such that 4*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (41*10^n+13)/9 is prime.
%C a(22) > 10^5. - _Robert Price_, May 22 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/45557.htm#prime">Prime numbers of the form 455...557</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101727(n) + 1.
%t Do[ If[ PrimeQ[(41*10^n + 13)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101727.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 17 2005
%E Addition of a(21) from Kamada data by _Robert Price_, Dec 09 2010
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