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%I #22 Jul 08 2021 01:21:15
%S 2,12,30,60,116,290,632,1064,1494,5432,7362
%N Numbers k such that 8*R_k + 3*10^k - 5 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
%C Also, numbers k such that (35*10^k - 53)/9 is prime.
%C Terms from Kamada data.
%C a(12) > 10^5.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/abbba.htm">Near-repdigit numbers of the form ABB...BBA</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/38883.htm#prime">Prime numbers of the form 388...883</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%e For k=2, 8*R_2 + 3*10^k - 5 = 88 + 300 - 5 = 383 which is prime.
%t Select[Range[100000], PrimeQ[(35*10^#-53)/9] &] (* adapted by _Vincenzo Librandi_, Jun 19 2015 *)
%Y Cf. A002275.
%K more,hard,nonn
%O 1,1
%A _Robert Price_, Jun 18 2015
%E Corrected Mathematica code from _Vincenzo Librandi_, Jun 19 2015
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