 Solution

ID: past-exam-of-the-probability-statistics-and-options-ii-course-of-the-university-of-oxford/2009/c/c2/iii/solution

p ∤ a

and

m

is the number of least positive residue classes among

a, 2 a, \dots, ((p - 1) /2) a

that exceed

p /2

, then

(a / p) = (- 1)^{m}

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