A336719 - OEIS

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

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OFFSET

2,1

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

PROG

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