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 A249330 #9 Sep 08 2022 08:46:10 %S A249330 2,5,7,13,17,19,23,29,31,43,47,59,61,67,71,73,89,97,101,103,109,113, %T A249330 127,131,137,139,149,151,157,163,167,179,181,191,193,197,199,211,223, %U A249330 229,233,241,251,257,263,269,277,281,283,293,307,311,313,331,337,349,353 %N A249330 Primes which do not divide any repunit number R(p) = (10^p - 1)/9 with p prime. %C A249330 If a prime p has period n, then p divides 10^m - 1 for all m divisible by n. Therefore the sequence together with 3 is the complement in the primes of A072859. %o A249330 (Magma) [2] cat [p: p in PrimesInInterval(5, 353) | not IsPrime(Modorder(10, p))]; %Y A249330 Cf. A072859. %K A249330 nonn,base %O A249330 1,1 %A A249330 _Arkadiusz Wesolowski_, Oct 25 2014