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 A103067 #16 Aug 17 2025 12:42:21
%S A103067 1,4,18,28,55,1728,1876,1884,6841,10782,25366,98446,137250
%N A103067 Numbers k such that 7*10^k + 8*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C A103067 Also numbers k such that (71*10^k+1)/9 is prime.
%H A103067 Makoto Kamada, <a href="https://stdkmd.net/nrr/7/78889.htm#prime">Prime numbers of the form 788...889</a>.
%H A103067 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A103067 a(n) = A101153(n) + 1.
%t A103067 Do[ If[ PrimeQ[(71*10^n + 1)/9], Print[n]], {n, 0, 10000}]
%Y A103067 Cf. A002275, A101153.
%K A103067 more,nonn
%O A103067 1,2
%A A103067 _Robert G. Wilson v_, Jan 19 2005
%E A103067 a(10)-a(13) from Kamada data by _Robert Price_, Dec 14 2010