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%I #24 Sep 08 2022 08:45:16
%S 2,6,8,20,108,288,306,462,20102,30042,69050
%N Numbers n such that 5*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (53*10^n-17)/9 is prime.
%C a(12) > 10^5. - _Robert Price_, Sep 07 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/5/58887.htm#prime">Prime numbers of the form 588...887</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101588(n) + 1.
%t Do[ If[ PrimeQ[(53*10^n - 17)/9], Print[n]], {n, 0, 10000}]
%t Select[Range[0, 10000], PrimeQ[(53 10^# - 17)/9] &] (* _Vincenzo Librandi_, Sep 08 2015 *)
%o (Magma) [n: n in [0..350] | IsPrime((53*10^n-17) div 9)]; // _Vincenzo Librandi_, Sep 08 2015
%Y Cf. A002275, A101588.
%K more,nonn
%O 1,1
%A _Robert G. Wilson v_, Jan 18 2005
%E Addition of a(9) from Kamada data by _Robert Price_, Dec 13 2010
%E a(10) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
%E a(11) from _Robert Price_, Sep 07 2015
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