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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 ยง 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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