Write something below ampersand sign

Question

I need to write something below and top of ampersand sign. I want it to be like \sum. I have tried

\&_{i = 0}^{n}

but it shows i=0 in the index but not below ampersand sign.

Answer 1

\documentclass{report}

\DeclareMathOperator*{\amper}{\&}

\begin{document}
Inline: $\amper_{i=1}^n$

Inline with display: $\amper\limits_{i=1}^n$

Display: \[ \amper_{i=1}^n \] 
\end{document}

Answer 2

If you wanted the ampersand to display larger in display style, you can use scalerel package to grow the size to match the vertical extent of the \sum sign.

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator*{\foo}{\scalerel*{\&}{\sum}}
\usepackage{scalerel}
\begin{document}
\[ \foo_{i=3}^{6}(f^2(i)) \]
\centering This is inline: \(\foo_{i=3}^{6}(f^2(i)) \)
\end{document}