  We derive generalized Luscher formulas for finite size corrections in a
theory with a general dispersion relation. For the AdS_5xS^5 superstring these
formulas encode leading wrapping interaction effects. We apply the generalized
mu-term formula to calculate finite size corrections to the dispersion relation
of the giant magnon at strong coupling. The result exactly agrees with the
classical string computation of Arutyunov, Frolov and Zamaklar. The agreement
involved a Borel resummation of all even loop-orders of the BES/BHL dressing
factor thus providing a strong consistency check for the choice of the dressing
factor.
