A particular type of automorphism group which exists only for groups. For a group 
,
the outer automorphism group is the quotient group 
,
which is the automorphism group of 
modulo its inner automorphism
group.
Outer Automorphism Group
See also
Automorphism Group, Inner Automorphism Group, Quotient GroupExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Outer Automorphism Group." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/OuterAutomorphismGroup.html