# Mathjax format for combinatorials

Could someone direct me to a source that explains how to format combinatorial expressions, eg rCn in Mathjax? Like.

n
r

thanks ralph

• You can use commands such as $\binom{n+1}k$\binom{n+1}k$, $\dbinom{n+1}k $\dbinom{n+1}k$, $\tbinom{n+1}k$\tbinom{n+1}k – Martin Sleziak Feb 8 at 5:27
• BTW in case of problems with MathJax, you're welcome to ask also in the MathJax chatroom. – Martin Sleziak Feb 9 at 9:01

You have asked specifically about binomial coefficients. They can be typeset using \binom or \choose. Examples: $\binom{m+n}{k+1}$ $$\binom{m+n}{k+1}$$ or ${m+n \choose k+1}$ $${m+n \choose k+1}$$. In the case of choose do not forget to include curly brackets around the binomial coefficient. The command \binom comes also with two size modifications: $\dbinom{m+n}{k+1}$ $$\dbinom{m+n}{k+1}$$ and $\tbinom{m+n}{k+1}$ $$\tbinom{m+n}{k+1}$$. (Using \dbinom in titles is discouraged because it makes the vertical size too big: Guidelines for good use of $$\rm\LaTeX$$ in question titles.)
You can typeset multinomial coefficients in a similar way: $\binom n{k_1, k_2, \ldots, k_m}$ $$\binom n{k_1, k_2, \ldots, k_m}$$.
On Wikipedia, some common symbols used in combinatorics are listed in the article List of mathematical symbols by subject § Combinatorics (current revision). The article also briefly mentions LaTeX syntax. Among the symbols linked there you have factorial and its modification, it this case the syntax is clear: $n!$ $$n!$$, $n!!$ $$n!!$$, $!n$ $$!n$$. For multinomial coefficients, Wikipedia uses $\left(\!\!\binom nk\!\!\right)$ $$\left(\!\!\binom nk\!\!\right)$$ and it seems that there are also posts on this site which use the same notation. The Wikipedia article also mentions falling and rising factorials: $n^{\overline{m}}$ $$n^{\overline{m}}$$ and $n^{\underline{m}}$ $$n^{\underline{m}}$$. And also primorial $n\#$ $$n\#$$.
Another symbol in combinatorics I am able to think of is the symbol for Stirling numbers: $\left[{n \atop k}\right]$ $$\left[{n \atop k}\right]$$ and $\left\{\begin{matrix} n \\ k \end{matrix}\right\}$ $$\left\{\begin{matrix} n \\ k \end{matrix}\right\}$$.
One way, which might often help to find appropriate MathJax/LateX syntax, could be checking how the things are typeset in other posts on this site. (For example, in this case you could have looked at the posts tagged . See also: How to view LaTeX source of equations?.) And also if you can find a corresponding article on Wikipedia and if the symbols/formulas are typeset there using $..$, the same syntax is very likely to work in MathJax/LaTeX. (To view source code of the Wikipedia article, you can simply click on edit.)