For the number of combinations with repetitions a symbol similar to the binomial coefficient is used with additional parentheses:
What would be the proper way how to type the symbol in LaTeX? I was thinking of adding \left( and \right) to {n\choose k}, but it doesn't seem right.
Update: Also I'd be interested how to type it in MathJax, if possible.

\left(\!\!\!\binom{n}{k}\!\!\!\right)... – crateane Jul 25 '15 at 13:05\newcommand{\mybinom}[2]{\left(\mkern -10mu \binom{#1}{#2}\mkern -10mu \right)}but for sure does not work on inline. – Sigur Jul 25 '15 at 13:10