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 A111974 #20 Jul 18 2025 04:05:04 %S A111974 3,7,19,163,487,1459,39367,86093443,258280327,411782264189299, %T A111974 116299474006080119380780339,3140085798164163223281069127, %U A111974 84782316550432407028588866403,20602102921755074907947094535687,1910009901593650473786381403548828023839870277948686259673707683 %N A111974 Primes of the form 2*3^k + 1. %H A111974 Amiram Eldar, <a href="/A111974/b111974.txt">Table of n, a(n) for n = 1..23</a> %H A111974 Hartosh Singh Bal and Gaurav Bhatnagar, <a href="https://arxiv.org/abs/1903.09619">Prime number conjectures from the Shapiro class structure</a>, arXiv:1903.09619 [math.NT], 2019-2020. %F A111974 a(n) = A052919(A003306(n)+1). - _Amiram Eldar_, Jul 18 2025 %t A111974 Select[2*3^Range[100]+1, PrimeQ] %Y A111974 Cf. A003306 (k such that 2*3^k + 1 is prime), A003307 (k such that 2*3^k - 1 is prime), A052919. %K A111974 nonn %O A111974 1,1 %A A111974 _T. D. Noe_, Aug 24 2005 %E A111974 a(15) from _Amiram Eldar_, Jul 18 2025