Cofactorial automorphism

Definition

For a finite group

An automorphism $\sigma$ of a finite group $G$ is termed a cofactorial automorphism for $G$ if every prime dividing the order of $\sigma$ (viewed as an element of the automorphism group of $G$) also divides the order of $G$.

For a periodic group

An automorphism $\sigma$ of a periodic group $G$ is termed a cofactorial automorphism for $G$ if every prime dividing the order of $\sigma$ equals the order of some non-identity element of $G$.

For a group with elements of infinite order

If the group has any element of infinite order, then every automorphism of the group is considered to be a cofactorial automorphism.

Relation with other properties

Stronger properties

• Inner automorphism
• Stability automorphism

Weaker properties

• Automorphism

Related subgroup properties

• Cofactorial automorphism-invariant subgroup
• Sub-cofactorial automorphism-invariant subgroup
• Subgroup-cofactorial automorphism-invariant subgroup