If 1,000 mod n =1, where n=1, 2, 3,4...........998, 999, 1000, just how many n are there between 1 and 1,000?
\(\text{Since $1000 \pmod 1 = 0$ and $1000 \pmod {1000} = 0$, $n$ can only be $2,3, \ldots , 999$.} \)
\(\begin{array}{|rcll|} \hline 1000 & \equiv & 1 \pmod n \\ \text{or} \\ 1000-1 &=& n\cdot m,~ \text{with } m \in \mathbb{Z} \\ 999 &=& n\cdot m,~ \text{so $n$ are all divisors of $999$ except $1$ } \\ \hline \end{array} \)
The divisors of 999 are:
Divisors:
1 | 3 | 9 | 27 | 37 | 111 | 333 | 999 (8 divisors)
n = 3 | 9 | 27 | 37 | 111 | 333 | 999 (7 numbers)
