It is asked to find the interval of convergence of the power series
$$\sum \left(1+ \frac{2}{n}\right)^{n^3 + n^2 +1}x^{n^2}$$
But how should I write this series so it has the form
$$\sum a_n(x-c)^n?$$
With the given formula, I don't know if I can call
$$a_n=\left(1+ \frac{2}{n}\right)^{n^3 + n^2 +1}$$
Thanks in advance!