This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A102989 #22 Jan 17 2019 13:44:07
%S A102989 1,3,5,6,8,15,26,53,60,97,183,205,302,396,456,467,607,828,1860,2743,
%T A102989 4273,4781,5712,6038,6637,9222,10832,18865,25848,42247,48547,87565,
%U A102989 95588
%N A102989 Numbers n such that 4*10^n + 3*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C A102989 Also numbers n such that (13*10^n+11)/3 is prime.
%C A102989 a(34) > 10^5. - _Robert Price_, May 11 2015
%H A102989 Makoto Kamada, <a href="https://stdkmd.net/nrr/4/43337.htm#prime">Prime numbers of the form 433...337</a>.
%H A102989 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A102989 a(n) = A101724(n) + 1.
%t A102989 Do[ If[ PrimeQ[(13*10^n + 11)/3], Print[n]], {n, 0, 10000}]
%Y A102989 Cf. A002275, A101724.
%K A102989 more,nonn
%O A102989 1,2
%A A102989 _Robert G. Wilson v_, Jan 17 2005
%E A102989 Addition of a(27)-a(29) from Kamada data by _Robert Price_, Dec 08 2010
%E A102989 a(30)-a(31) from Erik Branger, May 01 2013, submitted by _Ray Chandler_, Aug 16 2013
%E A102989 a(32)-a(33) from _Robert Price_, May 11 2015