%I #19 Jan 17 2019 13:44:07
%S 0,1,2,3,4,15,27,71,86,105,242,250,448,539,784,814,1025,1172,1353,
%T 3009,3175,3682,6993,7612,7780,9633,27109,27735,28767,61574
%N Numbers n such that 9*10^n + 3*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (28*10^n+11)/3 is prime.
%C a(31) > 10^5. - _Robert Price_, Nov 07 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/93337.htm#prime">Prime numbers of the form 933...337</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101005(n-1) + 1, for n>1.
%e For n=0, (28*10^n+11)/3 = 13, which is prime.
%t Do[ If[ PrimeQ[(28*10^n + 11)/3], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101005.
%K more,nonn
%O 1,3
%A _Robert G. Wilson v_, Jan 19 2005
%E a(26)-a(28) from Kamada data by _Robert Price_, Dec 14 2010
%E Inserted a(1)=0 and added a(30) by _Robert Price_, Nov 07 2015
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