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%I #22 Sep 08 2022 08:45:16
%S 1,4,7,9,19,22,70,102,121,123,235,360,594,1614,2410,16048,16174
%N Numbers n such that 8*10^n + R_n + 8 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (73*10^n+71)/9 is prime.
%C a(18) > 10^5. - _Robert Price_, Oct 13 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/81119.htm#prime">Prime numbers of the form 811...119</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101060(n) + 1.
%t Do[ If[ PrimeQ[(73*10^n + 71)/9], Print[n]], {n, 0, 10000}]
%t Select[Range[0, 100000], PrimeQ[(73 10^# + 71)/9] &] (* _Vincenzo Librandi_, Oct 14 2015 *)
%o (Magma) [n: n in [0..400] | IsPrime((73*10^n+71) div 9)]; // _Vincenzo Librandi_, Oct 14 2015
%Y Cf. A002275, A101060.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 19 2005
%E a(16)-a(17) from Kamada data by _Robert Price_, Dec 14 2010
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