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%I #20 Sep 08 2022 08:45:16
%S 1,6,9,15,24,48,73,75,97,249,273,2488,14499,74773,87448
%N Numbers n such that 3*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (32*10^n-41)/9 is prime.
%C a(16) > 10^5. - _Robert Price_, May 24 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/35551.htm#prime">Prime numbers of the form 355...551</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101835(n) + 1.
%t Do[ If[ PrimeQ[(32*10^n-41)/9], Print[n]], {n, 0, 10000}]
%t Select[Range[0, 10000], PrimeQ[(32 10^# - 41)/9] &] (* _Vincenzo Librandi_, May 25 2015 *)
%o (Magma) [n: n in [0..2000] | IsPrime((32*10^n-41) div 9)]; // _Vincenzo Librandi_, May 25 2015
%Y Cf. A002275, A101835.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 17 2004
%E Addition of a(13) from Kamada data by _Robert Price_, Dec 13 2010
%E a(14)-a(15) from _Robert Price_, May 24 2015