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Numbers n such that 6*10^n + 8*R_n - 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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%I #16 Jan 17 2019 13:44:07

%S 2,3,8,50,56,72,108,132,182,1100,1368,1605,5132,22682

%N Numbers n such that 6*10^n + 8*R_n - 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (62*10^n-53)/9 is prime.

%C a(15) > 10^5. - _Robert Price_, Sep 15 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/6/68883.htm#prime">Prime numbers of the form 688...883</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%F a(n) = A101538(n) + 1.

%t Do[ If[ PrimeQ[(62*10^n - 53)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101538.

%K more,nonn

%O 1,1

%A _Robert G. Wilson v_, Jan 18 2005

%E a(14) from Kamada data by _Robert Price_, Dec 14 2010