Automorphisms of Automorphism Groups of Free
Martin R. Bridson and Karen Vogtmann
Journal of Algebra,
229 (2000), 785--792
For $n\geq 3$, the groups
$Out(F_n)$ and $Aut(F_n)$ are complete, i.e. they
are centreless and all of their automorphisms are inner.
- .pdf file (9 pages)
Shortly after writing this paper we noticed that the
same proof shows that the groups
$Out(F_n)$ and $Aut(F_n)$ are co-Hopf.