How to prove following statement :
Conjecture :
Let $n$ be an Idoneal number with property : $n \equiv 0 \pmod 4$ , and let $q$ be a prime number with
property : $q \equiv a \pmod n$ , $a \in \mathbb N$ , expressible as $q=\sqrt{x^2+n\cdot y^2}$ ; $x,y > 0$
then every odd prime $p$ such that : $p^2>n$ and $p\equiv a \pmod n$ can be expressed as :
$p=\sqrt{x^2+n\cdot y^2}$ ; $x,y > 0$ .
For example :
$p=\sqrt{x^2+4\cdot y^2}$ if and only if : $p\equiv 1 \pmod 4$
$p=\sqrt{x^2+8\cdot y^2}$ if and only if : $p\equiv 1 \pmod 8$ or $p\equiv 3 \pmod 8$