Let $[ \cdot ]$ denote the greatest integer function and $f(x) = \lim_{n \to \infty} \frac{1}{n^3} \sum_{k=1}^n \left[ \frac{k^2}{3^x} \right]$. Then $12 \sum_{j=1}^{\infty} f(j)$ is equal to ........... .

$\lim _{n \rightarrow \infty} \left( \frac{\sqrt{1} + 2 \sqrt{2} + 3 \sqrt{3} + \ldots + n \sqrt{n}}{n^{5/2}} \right) = $

If $[x]$ denotes the greatest integer $\le x$,then $\mathop {\text{Limit}}\limits_{n \to \infty } \frac{1}{n^4} \left( [1^3 x] + [2^3 x] + \dots + [n^3 x] \right)$ equals

$\lim _{n \rightarrow \infty}\left[\frac{1}{n}+\frac{1}{n+1}+\frac{1}{n+2}+\ldots+\frac{1}{3 n}\right]=$

The value of $\lim _{n \rightarrow \infty} \prod_{r=1}^n\left(1+\frac{r^2}{n^2}\right)^{\frac{2 r}{n^2}}$ is equal to

Let $\lim _{n \rightarrow \infty} \sum_{r=1}^{n} \left( \frac{n}{\sqrt{n^4+r^4}} - \frac{2 n r^2}{(n^2+r^2) \sqrt{n^4+r^4}} \right) = \frac{\pi}{k}.$ Using only the principal values of the inverse trigonometric functions,then $k^2$ is equal to: