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Numbers n such that 6*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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%I #20 Jan 17 2019 13:44:07

%S 0,1,33,72,177,192,325,417,732,1362,13947,14887,32706,63954,64783,

%T 82377

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

%C Also numbers n such that (62*10^n-17)/9 is prime.

%C a(17) > 10^5. - _Robert Price_, Sep 15 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/6/68887.htm#prime">Prime numbers of the form 688...887</a>.

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

%F a(n) = A101539(n-1) + 1 for n>1.

%t Do[ If[ PrimeQ[(62*10^n - 17)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101539.

%K more,nonn

%O 1,3

%A _Robert G. Wilson v_, Jan 18 2005

%E a(11)-a(12) from Kamada data by _Robert Price_, Dec 14 2010

%E a(13) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013

%E Inserted a(1)=0 by _Robert Price_, Sep 15 2015

%E a(14)-a(16) from _Robert Price_, Sep 15 2015