Summation symbol and fraction in LaTeX

\[
\frac{ \sum_{k=1}^{n} k^2 }{ 5 }
\]

\[ \frac{ \sum_{k=1}^{n} k^2 }{ 5 } \]

\[
\frac{ \sum\limits_{k=1}^{n} k^2 }{ 5 }
\]

\[ \frac{ \sum\limits_{k=1}^{n} k^2 }{ 5 } \]

LaTeX sum

LaTeX