On the nilpotent length of finite soluble groups with given normalizers of Sylow subgroups

for any s-closed local subformation F of the formation of all phi -dispersive metanilpotent groups,we prove that the nilpotent length of any finite soluble group G is at most 2s + 2 if the order of G is divisible by three distinct primes and the normalizers of all the Sylow subgroups of G belong to 3,where p(s) is the highest power of the phi -smallest prime p dividing \G/G(F)\ (where G(F) is the F-residual of G).