We consider the family of polynomials
$$\left\{ \begin{array}{l} H_0 = 1 \\ H_k = \frac{1}{k!} \prod_{j=0}^{k-1} (X - j) \quad \text{for } k \in \llbracket 1, n \rrbracket \end{array} \right.$$
Show that the family $\left(H_k\right)_{k \in \llbracket 0, n \rrbracket}$ is a basis of $\mathbb{R}_n[X]$.