N-abelian group

This group property is natural number-parametrized, in other words, for every natural number, we get a corresponding group property

Definition

Suppose $n$ is an integer. A group $G$ is termed a $n$-abelian group if the $n^{th}$ power map $x \mapsto x^n$ is an endomorphism of $G$, i.e., $(xy)^n = x^ny^n$ for all $x,y \in G$. If this is the case, then the $n^{th}$ power map is termed a universal power endomorphism of $G$.

As noted below, n-abelian iff (1-n)-abelian, so it suffices to restrict attention to $n$ a positive integer.

Alternative definitions

See Alperin's structure theorem for n-abelian groups.

Facts

General facts

• n-abelian iff (1-n)-abelian
• The set of $n$ for which $G$ is $n$-abelian is termed the exponent semigroup of $G$. It is a submonoid of the multiplicative monoid of integers.
• abelian implies n-abelian for all n
• n-abelian implies every nth power and (n-1)th power commute
• n-abelian implies n(n-1)-central
• n-abelian iff abelian (if order is relatively prime to n(n-1))
• nth power map is surjective endomorphism implies (n-1)th power map is endomorphism taking values in the center
• (n-1)th power map is endomorphism taking values in the center implies nth power map is endomorphism
• Frattini-in-center odd-order p-group implies p-power map is endomorphism
• Frattini-in-center odd-order p-group implies (mp plus 1)-power map is automorphism
• Characterization of exponent semigroup of a finite p-group
• Alperin's structure theorem for n-abelian groups

Particular values

Value of $n$ (note that the condition for $n$ is the same as the condition for $1-n$)	Characterization of $n$-abelian groups	Proof	Other related facts
0	all groups	obvious
1	all groups	obvious
2	abelian groups only	2-abelian iff abelian	endomorphism sends more than three-fourths of elements to squares implies abelian
-1	abelian groups only	-1-abelian iff abelian
3	3-abelian group means: 2-Engel group and derived subgroup has exponent dividing three	Levi's characterization of 3-abelian groups	cube map is surjective endomorphism implies abelian, cube map is endomorphism iff abelian (if order is not a multiple of 3), cube map is endomorphism implies class three
-2	same as for 3-abelian	(based on n-abelian iff (1-n)-abelian)

Relation with other properties

Weaker properties

• n-nilpotent group
• n-solvable group