Given number: k3 It is a series of species ak(cx−x0)dk - power series. The radius of convergence of a power series can be calculated by the formula: Rd=cx0+limk→∞ak+1ak In this case ak=k3 and x0=0 , d=0 , c=1 then 1=k→∞lim((k+1)3k3) Let's take the limit we find