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%I #28 Jul 13 2023 12:26:19
%S 1,2,3,4,8,11,13,24,28,52,54,94,297,657,1006,5347,8189,9314,23055,
%T 53287,64807,218644
%N Numbers k such that 2*10^k + 3*R_k + 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also numbers k such that (7*10^k + 17)/3 is prime.
%C a(23) > 3*10^5. - _Robert Price_, Jul 13 2023
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/2/23339.htm#prime">Prime numbers of the form 233...339</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101956(n) + 1. - _Robert Price_, Nov 25 2014
%t Do[ If[ PrimeQ[(7*10^n + 17)/3], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101956.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 17 2004
%E Addition of a(19) from Kamada data by _Robert Price_, Dec 10 2010
%E a(20)-a(21) from Kamada data by _Robert Price_, Nov 25 2014
%E a(22) from _Robert Price_, Jul 13 2023
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