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%I #19 Jan 17 2019 13:44:07
%S 0,6,15,36,45,447,1031,1239,3492,6069,13647,17238,56271,72711,75381
%N Numbers n such that 9*10^n + 7*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (88*10^n-43)/9 is prime.
%C a(16) > 10^5. - _Robert Price_, Nov 12 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/97773.htm#prime">Prime numbers of the form 977...773</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101015(n-1) + 1, for n>1.
%t Do[ If[ PrimeQ[(88*10^n - 43)/9], Print[n]], {n, 0, 10000}]
%o (PARI) is(n)=isprime(9*10^n + 7*((10^n-1)/9) - 4) \\ _Anders Hellström_, Nov 12 2015
%Y Cf. A002275, A101015.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 19 2005
%E a(11)-a(12) from Kamada data by _Robert Price_, Dec 14 2010
%E Inserted a(1)=0 and added a(13)-a(15) from _Robert Price_, Nov 12 2015
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