The automorphism group AutF(n) of a free group F-n of rank a acts on t
he product of a copies of a group G by substituting a elements of G in
to the words defining an automorphism of the free group. This gives ri
se to an antihomomorphism from AutF(n) to a permutation group. We dete
rmine this antihomomorphic image of AutF(n) when G is the semidirect p
roduct Z(p) x Z(p).