@rahul sharma 5
I think something is wrong with formula given in the question, there should be $$(a_{n})^{n}$$
I thought so because formula for
$$e^{-x} = 1 + \frac{-x}{1!} + \frac{(-x)^{2}}{2!} + \frac{(-x)^{3}}{3!} + ........$$
or is it just some different $a_{n}$ idk?