I would like clarification\intuition about the set of least residues mod p, and the integer $\mu$.
Definition: Consider S= {$ -(p-1)/2, -(p-3)/2,\cdots ,-1,1,2,\cdots ,(p-1)2 $}.This is called the set of least residues $\mod{p}$
If p does not divide a, let $\mu$ be the number of negative least residues of the integers a,2a,3a,...,(p-1)(1/2)a.
Also, is there an easy way to calculate $\mu$ or is it just used in proofs?