Is there a way to show `\sum`

limits partially in inline mode and partially in display mode? I want to write:

```
\begin{equation}
\sum_{n=-\infty}^{+\infty} [...]
\end{equation}
```

but this way the lower limit is too wide, and I don’t like it. So I was hoping to write something like this:

```
\begin{equation}
\sum_{-\infty}^{+\infty}\nolimits_{n} [...]
\end{equation}
```

to write the index n on the right side of the sum symbol, while the limits of the summation remain above and below.

Of course it doesn’t work, LaTeX is pissed because there is a double subscript. Anyone knows if it’s possible to do what I want to?

In this instance a better approach would be to use mathtools’s \mathclap, which provides a centred overlap in math mode. The centred overlap implies a zero-width box containing stuff that overlaps on the left and right:

enter image description here

\documentclass{article}

\usepackage{mathtools}% http://ctan.org/pkg/mathtools

\begin{document}

\begin{align*}

A &= \sum_{n=-\infty}^{+\infty} f(x) \\

B &= \smashoperator[r]{\sum_{n=-\infty}^{+\infty}} f(x) \\

C &= \sum_{\mathclap{n=-\infty}}^{+\infty} f(x) \\

D &= \sum_{\substack{n={}\\-\infty}}^{+\infty} f(x) \\

E &= \sum_{-\infty}^{\infty}\mathop{}_{\mkern-5mu n} f(x)

\end{align*}

\end{document}

Sure mathtools also loads amsmath, but both these provide excellent tools in terms of typesetting mathematical content (and otherwise).

To add multiple things under a math operator (like \sum), see How do you put multiple things under a limit?, which suggests \substack (as I’ve done in the last horrible visual).