**1. The problem statement, all variables and given/known data**
Suppose p is a prime number. Prove that p is irreducible in Z[√−5] if and only if there does not exist α ∈ Z[√−5] such that N(α) = p.
Using this, find the smallest prime number that is not irreducible in Z[√−5]. **2. Relevant equations**
α = a+b√−5 ∈ Z[√−5]
N(α) = a2 + 5b2
N(α)N(β) = N(αβ) **3. The attempt at a solution**
I did => so I'm now doing <=
(Contraposition)Suppose that p is reducible in Z√-5 and isn't prime, then we know that p can be a product of two numbers: call them x,y ∈ Z√-5. Then we get that N(P)=n(x,y)=n(x)n(y)=(a^{2}+5b^{2})(c^{2}+5d^{2})
then i have no idea what to do |