What Is the Smallest Integer d Such That a^d Equals 1 Mod n?

[cutesteph]

Homework Statement

For any positive integer d and n, find the first integer d such that a^d =1 mod n

Homework Equations

Euler's totient function phi(n) = # of #s relatively prime to n
Will solve the condition if a and n are coprime but not for the first d

The Attempt at a Solution

If a and n are not coprime then there is no solution.
I am not sure how to find the smallest d such the condition holds. I know that d will be a factor of Euler's totient function.

 

[BvU]

For any positive integer d and n, find the first integer d such that a^d =1 mod n

Is d given or is d to be found ? Is a arbitrary ? Or would the exercise have been something along the lines of

For any positive integer a and n, find the first integer d such that a^d =1 mod n

 

[cutesteph]

d is to be found. Essentially I want to find the smallest integer d such that a^d = 1 mod n holds true.
Yes, For any positive integer a and n, find the first integer d such that a^d =1 mod n is how the problem should have been stated.