  We discuss the issue of how precisely we can measure the primordial power
spectrum by using future observations of 21 cm fluctuations and cosmic
microwave background (CMB). For this purpose, we investigate projected
constraints on the quantities characterizing primordial power spectrum: the
spectral index n_s, its running alpha_s and even its higher order running
beta_s. We show that future 21 cm observations in combinations with CMB would
accurately measure above mentioned observables of primordial power spectrum. We
also discuss its implications to some explicit inflationary models.
