Symmetric groups on finite sets are complete
For , the group is not centerless, but every automorphism is inner.
For , the group is centerless, but not every automorphism is inner. In fact, the symmetric group of degree six is of index two in its automorphism group.
- Symmetric groups on infinite sets are complete
- Automorphism group of alternating group equals symmetric group: This again holds under the same assumptions: .
- Centerless: The fact that the symmetric group is centerless for follows from fact (1).
- Every automorphism is inner: Fact (2) yields that every automorphism preserves the conjugacy class of transpositions when follows from fact (2). Fact (3) then yields that, in fact, every automorphism is inner.