Let f: R → R be a function defined by f(x)=x/((1+x^4)^1 / 4), and g(x)=f(f(f(f(x)))). Then, 18 ∫_0^√(2 √ 5) x^2 g(x) d x is equal to

Let $\displaystyle f: \mathbb{R} \rightarrow \mathbb{R}$ be a function defined by $\displaystyle f(x)=\frac{x}{\left(1+x^4\right)^{1 / 4}}$, and $\displaystyle g(x)=f(f(f(f(x))))$. Then, $\displaystyle 18 \int_0^{\sqrt{2 \sqrt{5}}} x^2 g(x) d x$ is equal to