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%I #24 Jan 17 2019 13:44:07
%S 0,2,5,6,11,15,69,90,134,189,245,267,270,470,1575,2295,2507,3512,3825,
%T 6857,11022,11657,17499,35036,41966,50558,93062
%N Numbers n such that 6*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (58*10^n-13)/9 is prime.
%C a(28) > 10^5. - _Robert Price_, Sep 12 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/6/64443.htm#prime">Prime numbers of the form 644...443</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101528(n-1) + 1 for n>1.
%t Do[ If[ PrimeQ[(58*10^n - 13)/9], Print[n]], {n, 0, 10000}]
%o (PARI) is(n)=isprime(6*10^n + 4*(10^n-1)/9 - 1) \\ _Anders Hellström_, Sep 12 2015
%Y Cf. A002275, A101528.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 18 2005
%E a(21)-a(23) from Kamada data by _Robert Price_, Dec 14 2010
%E a(24)-a(25) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
%E Inserted a(1)=0 by _Robert Price_, Sep 12 2015
%E a(26)-a(27) from _Robert Price_, Sep 12 2015
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