Question: is 3 a primitive root of 7?
Answer: The remainders in the period, which are 3, 2, 6, 4, 5, 1, form a rearrangement of all nonzero remainders modulo 7, implying that 3 is indeed a primitive root modulo 7. This derives from the fact that a sequence (gk modulo n) always repeats after some value of k, since modulo n produces a finite number of values.