\documentclass[a4paper,11pt]{article}
\usepackage[polish]{babel}
\usepackage[utf8]{inputenc} 
\usepackage[T1]{fontenc}
\usepackage{fourier}
\usepackage{amsmath}
\usepackage{siunitx}


\sisetup{output-decimal-marker={,}}

\begin{document}

\noindent
\num{1234567890}\\
\num{12345.006789}\\
\num{1.23456e-7}\\
\num{1,23456e-7}\\
\num{.123456e-7}\\
\num{e6}

\end{document}