Question

For what value of n, does the expression 1+2+...+(n-1) = 0 (mod n)?​

Answer 1

Answer:

So a2 ≡. { 0 (mod 4). 1 (mod 4) . D. 2.1.3. If a, b are integers such that a ≡ b (mod p) ... If GCD(a, n) = 1, prove that there is an integer b such that ab = 1 ( mod n).