Linear growth in power law f(T) gravity

We provide for the first time the growth index of linear matter fluctuations of the power law f (T) proportional to (-T)(b) gravity model. We find that the asymptotic form of this particular f (T) model is gamma approximate to 6/11-6b, which obviously extends that of the ACDM model, gamma(A) approximate to 6/11. Finally, we generalize the growth index analysis of f (T) gravity in the case where gamma is allowed to vary with redshift.