Which of the following is a condition for x2+y2=nx^2 + y^2 = nx2+y2=n to have solutions?
Every prime factor p≡3(mod4)p \equiv 3 \pmod{4}p≡3(mod4) must have an even exponent in the prime factorization of nnn
nnn must be a perfect square
nnn must be prime
No condition exists