A336719 Largest odd prime p for which the order of 2 mod p is at most n.

3, 7, 7, 31, 31, 127, 127, 127, 127, 127, 127, 8191, 8191, 8191, 8191, 131071, 131071, 524287, 524287, 524287, 524287, 524287, 524287, 524287, 524287, 524287, 524287, 524287, 524287, 2147483647, 2147483647, 2147483647, 2147483647, 2147483647, 2147483647

Offset: 2

Author

Jeppe Stig Nielsen, Aug 01 2020

Keywords

• nonn

Comments

a(1) is undefined.

Changing "at most n" to "equal to n" in the definition gives A097406.

The first term that is not a Mersenne prime (A000668) is 4432676798593.

For a version without duplicates, see A336720. For a list of all n where a(n) increases, see A336721.

Links

• Jeppe Stig Nielsen, Table of n, a(n) for n = 2..251

Crossrefs

Cf. A000668, A005420, A014664, A097406, A336720, A336721.

Programs

PARI

re=0;for(n=2,+oo,p=vecmax(factor(2^n-1)[,1]);p>re&&re=p;print1(re,", "))