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Jacobi symbol

DEFINITION 7.1   Let $ m$ be a positive odd integer. Let us factor $ m$ :

$\displaystyle m=\prod_i p_i^{e_i}
$

where $ p_i$ are primes. Then for any $ n\in \mathbb{Z}$ , we define Jacobi symbols as follows

$\displaystyle {\left(\frac{n}{m}\right)}=
\prod_i{\left(\frac{n}{p_i}\right)}^{e_i}
$

We further define

$\displaystyle {\left(\frac{a}{p}\right)}= 0$$\displaystyle \text { if } a \in p\mathbb{Z}.
$

THEOREM 7.2 (quadratic reciprocity theorem)   For any positive odd integers $ n,m$ , we have

$\displaystyle \left(\frac{m}{n}\right)
\left(\frac{n}{m}\right)
=(-1)^{(m-1)(n-1)/4}.
$

THEOREM 7.3   Let $ n$ be a postive odd integer. Then:

  1. $ {\left(\frac{-1}{m}\right)}=(-1)^{(m-1)/2} $ .
  2. $ {\left(\frac{2}{m}\right)}=(-1)^{(m^2-1)/8} $ .

EXERCISE 7.1   $ p=113357$ is a prime. (You may use the fact without proving it.) Is there any integer $ n$ such that

$\displaystyle n^2=11351$    in $\displaystyle \mathbb{Z}/p \mathbb{Z}$$\displaystyle \text { ?}
$

If so, can you find such $ n$ ?



2007-06-07