  We carry out numerical investigations of the dynamics and perturbations in
the Nflation model of Dimopoulos et al. (2005). This model features large
numbers of scalar fields with different masses, which can cooperate to drive
inflation according to the assisted inflation mechanism. We extend previous
work to include random initial conditions for the scalar fields, and explore
the predictions for density perturbations and the tensor-to-scalar ratio. The
tensor-to-scalar ratio depends only on the number of e-foldings and is
independent of the number of fields, their masses, and their initial
conditions. It therefore always has the same value as for a single massive
field. By contrast, the scalar spectral index has significant dependence on
model parameters. While normally multi-field inflation models make predictions
for observable quantities which depend also on the unknown field initial
conditions, we find evidence of a `thermodynamic' regime whereby the predicted
spectral index becomes independent of initial conditions if there are enough
fields. Only in parts of parameter space where the mass spectrum of the fields
is extremely densely packed is the model capable of satisfying the tight
observational constraints from WMAP3 observations.
