LaTeX.org

With the following, I find an extra line number:

\documentclass{article}
\usepackage{lineno}
\usepackage{amsmath}
\linenumbers*[1]
\begin{document}
\begin{linenomath*}
\begin{align}
&a1& \nonumber \\
&a2& \nonumber
\end{align} \end{linenomath*}
\end{document}

texshop_image.png

Thoughts ...