[seqfan] Re: What's the better definition of A001134

[David Applegate]

The "history" link on A001134 shows the evolution of the definition:

2 is a quartic residue modulo $_p$.

Primes p such that 2 is a quartic residue modulo p.

Primes p such that 2 is a quartic residue modulo p, but not a
higher-order residue. (Don Reble's improvement)

Primes p such that the multiplicative order of 2 modulo p is (p-1)/4.

If you were asking for an explanation of the definition, rather than the
history, the multiplicative order of x modulo y is the n such that
x^n === 1 (mod y), but x^(n-1) !== 1 (mod y).

-Dave