A number 
is an 
th
root of unity if 
and a primitive 
th root of unity if, in addition, 
is the smallest integer of 
, ..., 
for which 
.
Primitive Root of Unity
See also
Principal Root of Unity, Root of UnityExplore with Wolfram|Alpha
References
Nagell, T. Introduction to Number Theory. New York: Wiley, p. 157, 1951.Referenced on Wolfram|Alpha
Primitive Root of UnityCite this as:
Weisstein, Eric W. "Primitive Root of Unity." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/PrimitiveRootofUnity.html