Primitive root
A primitive root of unity of order in a field
is an element
of
such that
and
for any positive integer
. The element
generates the cyclic group
of roots of unity of order
.
If in there exists a primitive root of unity of order
, then
is relatively prime to the characteristic of
. An algebraically closed field contains a primitive root of any order that is relatively prime with its characteristic. If
is a primitive root of order
, then for any
that is relatively prime to
, the element
is also a primitive root. The number of all primitive roots of order
is equal to the value of the Euler function
if
.
In the field of complex numbers, the primitive roots of order take the form
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where and
is relatively prime to
.
A primitive root modulo is an integer
such that
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for , where
is the Euler function. For a primitive root
, its powers
are incongruent modulo
and form a reduced residue system modulo
(cf. Reduced system of residues). Therefore, for each number
that is relatively prime to
one can find an exponent
for which
: the index of
with respect to
.
Primitive roots do not exist for all moduli, but only for moduli of the form
, where
is a prime number. In these cases, the multiplicative groups (cf. Multiplicative group) of reduced residue classes modulo
have the simplest possible structure: they are cyclic groups of order
. The concept of a primitive root modulo
is closely related to the concept of the index of a number modulo
.
Primitive roots modulo a prime number were introduced by L. Euler, but the existence of primitive roots modulo an arbitrary prime number was demonstrated by C.F. Gauss (1801).
References
[1] | S. Lang, "Algebra" , Addison-Wesley (1984) |
[2] | C.F. Gauss, "Disquisitiones Arithmeticae" , Yale Univ. Press (1966) (Translated from Latin) |
[3] | I.M. Vinogradov, "Elements of number theory" , Dover, reprint (1954) (Translated from Russian) |
Comments
References
[a1] | G.H. Hardy, E.M. Wright, "An introduction to the theory of numbers" , Oxford Univ. Press (1979) |
Primitive root. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Primitive_root&oldid=35731