  Let $p$ be an odd prime number. In this article, we study the number of
quadratic residues and non-residues modulo $p$ which are multiples of $2$ or
$3$ or $4$ and lying in the interval $[1, p-1]$, by applying the Dirichlet's
class number formula for the imaginary quadratic field $\mathbb{Q}(\sqrt{-p})$.
