Find the parts of the z-plane for which the following series is convergent:

∑[(1/n!)(z^n)] where n runs from 0 to ∞

Cauchy's radius: (1/R)=Lt (n->∞) [(1/n!)^(1/n)]

Changing variables as 1/n=t,the limit becomes (1/R)=Lt(t->0) [(t!)^t]

I am having the limit as 1 and hence,R=1...but the book says Since

[(n!)^(1/n)] behaves like n as n → ∞ we find lim[(1/n!)^(1/n)] = 0. Hence R = ∞ and the series is convergent for all z