%I #22 Feb 01 2023 23:45:12
%S 1,3,4,6,9,22,28,34,37,61,82,274,276,735,1443,2215,2968,3301,3883,
%T 3991,5152,8032,8946,46642,57691
%N Numbers k such that 10^k + 4*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also numbers k such that (13*10^k + 23)/9 is prime.
%C a(26) > 10^5. - _Robert Price_, Feb 19 2015
%C a(26) > 2*10^5. - _Tyler Busby_, Feb 01 2023
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/1/14447.htm#prime">Prime numbers of the form 144...447</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102016(n) + 1.
%t Do[ If[ PrimeQ[(13*10^n + 23)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A102016.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 16 2004
%E a(24) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
%E a(25) from _Robert Price_, Feb 19 2015