The LaTeX command for sum (∑) is \sum (summation).
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| Command | Package | Use it when |
|---|---|---|
\sum_{i=1}^{n} x_i recommended | none | Limits above and below in display math, to the side inline. |
\sum\limits_{i=1}^{n} x_i | none | Limits above and below even in inline math. |
\displaystyle\sum_{i=1}^{n} x_i | none | Full display size inside a line of text. |
\sum_{\substack{i < j \\ i \neq k}} a_{ij} | amsmath | A condition on two lines under the sign. |
Write \sum inside math mode, that is between $…$ for inline math or in a \[ … \] or equation block for display math. It is part of core LaTeX math, so no extra package is required.
$\sum_{k=1}^{n} k = \frac{n(n+1)}{2}$Open this example in the live preview: it renders as you type, with no compiler and no signup.
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Use \sum in math mode; it needs no extra package. For example, $\sum_{k=1}^{n} k = \frac{n(n+1)}{2}$.
None: \sum is built into LaTeX, so no extra package is required.
\Sigma is the Greek letter: it does not grow in display math and its limits go to the side. Write sums with \sum.