Deduce that, if $X$ admits a moment of order $n \left( n \in \mathbb { N } ^ { * } \right)$, then $X$ admits moments of order $k$ for all $k \in \llbracket 1 , n - 1 \rrbracket$.
Deduce that, if $X$ admits a moment of order $n \left( n \in \mathbb { N } ^ { * } \right)$, then $X$ admits moments of order $k$ for all $k \in \llbracket 1 , n - 1 \rrbracket$.