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 A343914 #11 May 09 2021 10:08:12 %S A343914 1,0,0,0,1,0,0,1,0,0,2,0,2,1,0,0,1,1,0,2,0,0,1,0,1,2,0,1,1,0,0,1,1,0, %T A343914 3,0,0,1,1,0,3,0,1,1,0,2,1,2,0,3,0,0,1,0,0,3,0,1,1,1,2,3,9,0,1,0,1,2, %U A343914 0,0,2,1,6,1,0,0,1,1,0,1,3,0,2,0,1,3,0 %N A343914 Riesel problem in base 3: a(n) is the smallest k >= 0 such that (2*n)*3^k-1 is prime, or -1 if no such k exists. %C A343914 31532322469 (A273987(3)/2) is the smallest n such that a(n) = -1. %H A343914 Wikipedia, <a href="https://en.wikipedia.org/wiki/Riesel_number">Riesel number</a> %e A343914 For n = 11: (2*11)*3^k-1 is prime for k = 2, with 2 being the smallest such k, so a(11) = 2. %o A343914 (PARI) a(n) = for(k=0, oo, if(ispseudoprime((2*n)*3^k-1), return(k))) %Y A343914 Cf. A040081 (base 2), A273987. %K A343914 sign %O A343914 1,11 %A A343914 _Felix Fröhlich_, May 04 2021