Let $S_n = \sum_{k=1}^n \frac{n}{n^2+kn+k^2}$ and $T_n = \sum_{k=0}^{n-1} \frac{n}{n^2+kn+k^2}$ for $n=1, 2, 3, \ldots$. Then,

$\lim _{n \rightarrow \infty} \frac{1}{n^{k+1}}\left[2^k+4^k+6^k+\ldots+(2 n)^k\right]=$

Evaluate the limit: $\lim _{n \rightarrow \infty} \frac{3}{n}\left\{1+\sqrt{\frac{n}{n+3}}+\sqrt{\frac{n}{n+6}}+\sqrt{\frac{n}{n+9}}+\ldots+\sqrt{\frac{n}{n+3(n-1)}}\right\}$

For $a \in R, |a| > 1$,let $\lim _{n \rightarrow \infty} \left( \frac{1+\sqrt[3]{2}+\ldots+\sqrt[3]{n}}{n^{7/3} \left( \frac{1}{(an+1)^2} + \frac{1}{(an+2)^2} + \ldots + \frac{1}{(an+n)^2} \right)} \right) = 54$. Then the possible value$(s)$ of $a$ is/are:
$(1) 8$ $(2) -9$ $(3) -6$ $(4) 7$

Let $S = \frac{2}{1} {}^{n}C_{0} + \frac{2^{2}}{2} {}^{n}C_{1} + \frac{2^{3}}{3} {}^{n}C_{2} + \ldots + \frac{2^{n+1}}{n+1} {}^{n}C_{n}$. Then, $S$ equals

$\operatorname{Lim}_{n \rightarrow \infty} \frac{\pi}{2 n}\left[\sin \frac{\pi}{2 n}+\sin \frac{2 \pi}{2 n}+\ldots+\sin \frac{\pi}{2}\right]=$