\documentclass{article}
\usepackage[pdftex,a3paper,margin=1pt,landscape]{geometry}
\newcommand\astsLua[1]{%
\directlua{
ret = ""
for i=1,#1 do
ret = ret .. "*"
end
tex.print("\noexpand\\def\noexpand\\asts{"..ret.."}")
}
}
\begin{document}
\astsLua{10000}
\end{document}