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 A366680 #13 Oct 17 2023 11:16:17
%S A366680 3,294277,735439
%N A366680 Numbers k such that (34^k + 1)/35 is prime.
%C A366680 These are the repunits in base -34.
%H A366680 Paul Bourdelais, <a href="https://listserv.nodak.edu/cgi-bin/wa.exe?A2=NMBRTHRY;417ab0d6.0906">A Generalized Repunit Conjecture</a>
%e A366680 3 is a term since (34^3 + 1)/35 = 1123 is a prime.
%t A366680 Do[ If[ PrimeQ[ (34^n+1)/35], Print[n]], {n, 0, 18000}]
%o A366680 (PARI) is(n) = my(q=(34^n+1)/35); (denominator(q)==1) && ispseudoprime(q);
%Y A366680 Cf. A185230.
%K A366680 nonn,bref,hard,more
%O A366680 1,1
%A A366680 _Paul Bourdelais_, Oct 16 2023