# Displaying the binomial coefficient symbol in math mode

The problem is caused by the symbol of binomial coefficient (symbol of Newton), often used in math:

{N}\choose{k}


In my document I have formula:

$$P(A) = \sum P(\{ (e_1,...,e_N) \}) = {N}\choose{k} \cdot p^kq^{N-k}$$


which is rendered as:

but should be:

• Are you using LaTeX or plain TeX? Commented Aug 11, 2013 at 14:14
• I am compiling pdfs from files by pdflatex. Commented Aug 11, 2013 at 14:20
• Is the symbol N really supposed to represent the physical unit for force (in which case you should render it in an upright rather than italic style), or are you using the symbol to denote an integer?
– Mico
Commented Aug 11, 2013 at 14:23
• I mean that I've cited the formula which is correct but pdflatex generate something which I don't want. I'm sorry, but I translated binomial coefficient directly from Polish. Sorry for misrepresentation. Commented Aug 11, 2013 at 14:28

To fix this, simply add a pair of braces around the whole binomial coefficient, i.e.

{N\choose k}


(The braces around N and k are not needed.)

However, as you're using LaTeX, it is better to use \binom from amsmath, i.e.

\binom{N}{k}


Further, it is not recommended to use $$...$$, see Why is $…$ preferable to $$? Last, I'll note that amsmath provides different commands for 'continuation dots', including \dotsc for triple dots between commas. \documentclass{article} \usepackage{amsmath} \begin{document} $P(A) = \sum P(\{ (e_1,\dotsc,e_N) \}) = \binom{N}{k} \cdot p^kq^{N-k}$ \end{document}  • What differs between \dots and \dotsc, with overleaf.com, the outputs are identical. Commented Mar 28, 2018 at 3:08 • @pzorba75 The output of \dots depends on what it is placed between, try for example \documentclass{article} \usepackage{amsmath} \begin{document} 1,\dots,n 1+\dots+n \end{document}. Read also section 4.3 in the amsmath manual. Commented Mar 28, 2018 at 6:28 Just add curly braces around it to separate it: $$ P(A) = \sum P(\{ (e_1,...,e_N) \})  =  {{N}\choose{k}} \cdot p^kq^{N-k}$$ That should fix it. • Hello @Lance Everhart! $$ ... $$ is obsolet. Use $...$  see l2tabu on page 6. Commented Mar 27, 2018 at 22:25 • Isn’t this exactly the same as the first line of the other answer? – GuM Commented Mar 27, 2018 at 22:25 • Hello @GuM! No. Before the braces { and } weren't escaped by the slash sign. Commented Mar 27, 2018 at 22:29 • @Su-47: I don’t want to seem obstinate, but the braces around (e_1,...,e_N) are correctly indicated as \{ and \} in the existing answer too… – GuM Commented Mar 27, 2018 at 23:18 • @Su-47 $$... is not obsolete, is TeX (and it should not be used in a LaTeX document, where you should use $...$). Commented Mar 28, 2018 at 3:10