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Use the enumitem
package and its label*
key-value option which appends it value to the parent label.
\documentclass{article}
\usepackage{enumitem}
\setlist[enumerate]{label*=\arabic*.}
\begin{document}
\begin{enumerate}
\item List 1
\begin{enumerate}
\item sub list 1
\item sub list 2
\begin{enumerate}
\item subsub list 1
\end{enumerate}
\end{enumerate}
\end{enumerate}
\end{document}
The number of compositions of $n$ into odd parts is $F_n$, the $n$th Fibonacci number. See, e.g., page 259 of this paper by Hoggatt and Lind.