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%I #17 Jan 17 2019 13:44:07
%S 0,2,156,1055,1997,8930,9563,19560,26838,63857
%N Numbers n such that 6*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 (61*10^n-43)/9 is prime.
%C a(11) > 10^5. - _Robert Price_, Sep 12 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/6/67773.htm#prime">Prime numbers of the form 677...773</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101535(n-1) + 1 for n>1.
%t Do[ If[ PrimeQ[(61*10^n - 43)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101535.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 18 2005
%E a(8)-a(9) from Kamada data by _Robert Price_, Dec 14 2010
%E Inserted a(1)=0 by _Robert Price_, Sep 12 2015
%E a(10) from _Robert Price_, Sep 12 2015
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