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 A057172 #32 Feb 16 2025 08:32:43 %S A057172 3,11,31,43,47,59,107,811,2819,4817,9601,33581,38447,41341,131891, %T A057172 196337,1313371 %N A057172 Numbers n such that (6^n + 1)/7 is a prime. %C A057172 a(15), a(16) and a(17) correspond to probable primes. %H A057172 P. Bourdelais, <a href="https://listserv.nodak.edu/cgi-bin/wa.exe?A2=NMBRTHRY;417ab0d6.0906">A Generalized Repunit Conjecture</a> %H A057172 J. Brillhart et al., <a href="http://dx.doi.org/10.1090/conm/022">Factorizations of b^n +- 1</a>, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002. %H A057172 H. Dubner and T. Granlund, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL3/DUBNER/dubner.html">Primes of the Form (b^n+1)/(b+1)</a>, J. Integer Sequences, 3 (2000), #P00.2.7. %H A057172 H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a> %H A057172 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Repunit.html">Repunit</a> %t A057172 Select[Range[5000], PrimeQ[(6^# + 1) / 7] &] (* _Vincenzo Librandi_, Oct 29 2017 *) %o A057172 (PARI) isok(n) = (denominator(p=(6^n+1)/7)==1) && isprime(p); \\ _Michel Marcus_, Oct 29 2017 %K A057172 nonn,more %O A057172 1,1 %A A057172 _N. J. A. Sloane_, Sep 15 2000 %E A057172 a(12) was discovered by Kamil Duszenko, Jul 15 2003 %E A057172 a(13) was discovered by _Henri Lifchitz_, Sep 15 2007 %E A057172 a(14) was discovered by _Paul Bourdelais_, Oct 01 2007 %E A057172 a(15) was discovered by _Paul Bourdelais_, Feb 01 2010 %E A057172 a(16) was discovered by _Paul Bourdelais_, Feb 19 2010 %E A057172 a(17) was discovered by _Paul Bourdelais_, Jan 28 2019