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 A263500 #23 Mar 04 2023 08:56:03 %S A263500 0,14,140324348,34,0,8,177744,32,14 %N A263500 Smallest positive b such that for all k >= 1 the numbers n*b^k + 1 are composite and gcd(n+1, b-1) = 1, or 0 if n > 1 is of the form 2^m - 1. %C A263500 a(2) = 131072, or it is a Sierpiński number multiplied by a power of 2. %C A263500 Because a(1) = 8 but a(2) is unknown, we do not include it here; we set the offset to 3. %C A263500 a(2) <= 201446503145165177. %H A263500 Dan Krywaruczenko, <a href="https://scholar.rose-hulman.edu/rhumj/vol9/iss2/4">A Reverse Sierpiński Number Problem</a>, Rose-Hulman Undergraduate Mathematics Journal: Vol. 9: Iss. 2, Article 4, 2009. %Y A263500 Cf. A123159. %K A263500 nonn,more,hard %O A263500 3,2 %A A263500 _Arkadiusz Wesolowski_, Oct 19 2015