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%I #15 Sep 08 2022 08:45:13
%S 3,13,113,11113,111111113,11111111113,111111111111111111111113,
%T 111111111111111111111111111111111111111111111111111111111111111111111111111111111113
%N Primes of the form 10*R_k + 3, where R_k is the repunit (A002275) of length k.
%C Primes of the form 2 + (10^k - 1)/9, k > 0. - _Vincenzo Librandi_, Dec 13 2011
%H Vincenzo Librandi, <a href="/A093011/b093011.txt">Table of n, a(n) for n = 1..9</a>
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/1/11113.htm#prime">Prime numbers of the form 11...113</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t Select[Table[(((10^n-1)/ 9)+2),{n,1,900}],PrimeQ] (* _Vincenzo Librandi_, Dec 13 2011 *)
%o (Magma) [a: n in [1..100] | IsPrime(a) where a is ((10^n-1) div 9)+2 ]; // _Vincenzo Librandi_, Dec 13 2011
%Y Cf. A056654 (corresponding k).
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Mar 14 2004