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 A336719 #12 Aug 25 2020 06:40:00 %S A336719 3,7,7,31,31,127,127,127,127,127,127,8191,8191,8191,8191,131071, %T A336719 131071,524287,524287,524287,524287,524287,524287,524287,524287, %U A336719 524287,524287,524287,524287,2147483647,2147483647,2147483647,2147483647,2147483647,2147483647 %N A336719 Largest odd prime p for which the order of 2 mod p is at most n. %C A336719 a(1) is undefined. %C A336719 Changing "at most n" to "equal to n" in the definition gives A097406. %C A336719 The first term that is not a Mersenne prime (A000668) is 4432676798593. %C A336719 For a version without duplicates, see A336720. For a list of all n where a(n) increases, see A336721. %H A336719 Jeppe Stig Nielsen, <a href="/A336719/b336719.txt">Table of n, a(n) for n = 2..251</a> %o A336719 (PARI) re=0;for(n=2,+oo,p=vecmax(factor(2^n-1)[,1]);p>re&&re=p;print1(re,", ")) %Y A336719 Cf. A000668, A005420, A014664, A097406, A336720, A336721. %K A336719 nonn %O A336719 2,1 %A A336719 _Jeppe Stig Nielsen_, Aug 01 2020