Ratio-Test Method for Radius of Convergence of $\sum _k^{\∞}{a}_k{x}^{r k\+\mathrm{\λ}}\,$$r$ and $\mathrm{\λ}$ fixed integers, $r$ and $a_k$ positive:

General term $a_k$

Enter $r$, the coefficient of $k$ in the power of $x$ in the general term:

Radius of Convergence