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

n
r

thanks ralph

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    $\begingroup$ 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 $\endgroup$ – Martin Sleziak Feb 8 at 5:27
  • $\begingroup$ BTW in case of problems with MathJax, you're welcome to ask also in the MathJax chatroom. $\endgroup$ – Martin Sleziak Feb 9 at 9:01
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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 $\left\{\begin{matrix} n \\ k \end{matrix}\right\}$ $\left\{\begin{matrix} n \\ k \end{matrix}\right\}$.

This is what I was able to think of from the top of my head - with some help of Wikipedia. (I am sure that people who are more experienced both in combinatorics and in LaTeX can add a lot of further details.)

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 <math>..</math>, 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.)

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