abstract algebra [primitive root mod n, euler theorem, fermat theorem]

Try this qn

Quote:

For a prime number p the set of co-primes less than or equal to it is given by {1,2,3,4,...p-1} .

We define f(x,p) 0<x<p = 1 if and only if all the numbers from 1 to p-1 can be written as a power of x in modulo-p arithmetic .

Let n be the largest 12-digit prime number . Find the product of all integers j less than n such that f(j,n)=1, in modulo-n arithmetic

n is 999999999989

The answer for this is 1.

How is it??

Please can anyone explain?