Definition (Jacobi symbol)
Let b∈Z and n∈N odd. We factor n as a unique product of prime powers: n=p1α1…prαrWe define the Jacobi Symbol as a product of Legendre symbols via (nb):=(p1b)α1…(prb)αr
Proposition
If n is odd then the satisfies (n−1)=(−1)2n−1
Proposition
If n is odd and positive, then (n2)=(−1)8n2−1
Theorem (Quadratic Reciprocity of Jacobi)
If m,n are coprime odd integers, then (nm)=(−1)4(m−1)(n−1)(mn)