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 A256396 #16 Oct 27 2024 12:17:35 %S A256396 2,5,7,11,13,19,29,37,53,59,61,67,79,83,97,101,103,107,131,139,149, %T A256396 163,173,179,181,193,197,199,211,227,269,271,293,307,313,317,347,349, %U A256396 367,373,379,389,409,419,421,439,443,461,463,467,487,491,499,509,523,541,547,557,563,577,587 %N A256396 Primes p such that p divides 3*2^k + 1 for some k >= 0. %C A256396 Also prime factors of the numbers 2^k + 3. %C A256396 Primes in A256397 do not belong to this sequence. %H A256396 Charles R Greathouse IV, <a href="/A256396/b256396.txt">Table of n, a(n) for n = 1..10000</a> %F A256396 A prime p is in the sequence if and only if -3 == 2^k (mod p). %o A256396 (PARI) is(n)=if(!isprime(n), return(0)); if(n<5, return(n==2)); my(m=Mod(2,n)); while(m!=1, if(m==-3, return(1),m*=2)); 0 \\ _Charles R Greathouse IV_, Jun 03 2015 %Y A256396 Supersequence of A001122 and A039687. %K A256396 nonn %O A256396 1,1 %A A256396 _Arkadiusz Wesolowski_, Jun 03 2015