VN-TST 1998 Problem 5

Let $d$ be a positive divisor of $5 + 1998^{1998}$ . Prove that $d = 2 \cdot x^2 + 2 \cdot x \cdot y + 3 \cdot y^2$ , where $x, y$ are integers if and only if $d$ is congruent to 3 or 7 $\pmod{20}$ .