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 A367648 #15 Jan 29 2025 08:15:56 %S A367648 2,13,109,433,757,3889,8209,17497,52489,58321,70957,1190701,1705861, %T A367648 2598157,6627097,13463173,57395629,23245229341,79320757897, %U A367648 1069604540569,1631815099669,5774114968057,8635817966221,23765922477217,43781455818469,307283335691329 %N A367648 Primes p such that the multiplicative order of 3 modulo p is a power of 3. %C A367648 Prime factors of numbers of the form 3^3^i - 1: p divides 3^3^i - 1 if and only if the multiplicative order of 3 modulo p is a power of 3 not exceeding 3^i. %e A367648 13 is a term since the multiplicative order of 3 modulo 13 is 3 = 3^1, which means that 13 is a factor of 3^3^1 - 1. %e A367648 109 is a term since the multiplicative order of 3 modulo 109 is 27 = 3^3, which means that 109 is a factor of 3^3^3 - 1. %o A367648 (PARI) isA367648(n) = isprime(n) && (n!=3) && isprimepower(3*znorder(Mod(3,n))) %Y A367648 Subsequence of A367265. %Y A367648 Cf. A023394 (ord(2,p) being a power of 2, prime factors of numbers of the form 2^2^i - 1 (or of the form 2^2^i + 1)), A367649 (ord(3,p) being 2 times a power of 3, prime factors of numbers of the form 3^3^i + 1). %K A367648 nonn,hard %O A367648 1,1 %A A367648 _Jianing Song_, Nov 25 2023 %E A367648 a(18)-a(19) from _Michel Marcus_, Nov 27 2023 %E A367648 a(20)-a(25) from _Max Alekseyev_, Jul 22 2024 %E A367648 a(26) from _Jinyuan Wang_, Jan 29 2025