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 A130325 #12 Feb 09 2025 10:24:46
%S A130325 2,2,2,2,5,2,2,3,11,17,2,23,29,3,5,3,43,2,7,17,19,3,11,23,13,19,19,7,
%T A130325 43,23,71,5,19,2,59,11,59,2,47,31,89,5,2,3,19,107,11,71,59,23,29,7,61,
%U A130325 89,2,173,11,17,37,37,31,23,19,2,199,103,59,37,139,17,67,41,43
%N A130325 Least prime p such that 3*p*2^n-1 is prime.
%H A130325 Pierre CAMI, <a href="/A130325/b130325.txt">Table of n, a(n) for n = 0..500</a>
%e A130325 3*2*2^0-1=5 is prime so for n=0 p=2.
%e A130325 3*2*2^1-1=11 is prime so for n=1 p=2.
%t A130325 s={};Do[ i=0;Until[PrimeQ[3Prime[i]*2^n-1],i++];AppendTo[s,Prime[i]] ,{n,0,72}];s (* _James C. McMahon_, Feb 08 2025 *)
%o A130325 (PARI) a(n) = my(p=2); while (!isprime(3*p*2^n-1), p=nextprime(p+1)); p; \\ _Michel Marcus_, Sep 23 2019
%Y A130325 Cf. A130326, A130327.
%K A130325 nonn
%O A130325 0,1
%A A130325 _Pierre CAMI_, May 24 2007