%I #17 Jan 17 2019 13:44:07
%S 3,4,24,39,63,76,108,166,520,1810,2349,2562,5784,6448,11692,16036,
%T 17554
%N Numbers n such that 9*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (83*10^n-11)/9 is prime.
%C a(18) > 10^5. - _Robert Price_, Nov 03 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/92221.htm#prime">Prime numbers of the form 922...221</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101001(n) + 1.
%t Do[ If[ PrimeQ[(83*10^n - 11)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101001.
%K more,nonn
%O 1,1
%A _Robert G. Wilson v_, Jan 19 2005
%E a(15)-a(17) from Kamada data by _Robert Price_, Dec 14 2010