The least quadratic residue and integers represented by quadratic forms

Kannan Soundararajan, João C. C. Vargas

Let $\ell (n)$ denote the least non-trivial reduced quadratic residue modulo $n$; that is, $\ell (n)$ denotes the smallest square-free integer $r>1$ with $(r,n)=1$ and $r\equiv x^2 \…