Positive integer not divisible by 7

Hi,

Is there a simple explanation for this?

The positive integer $\displaystyle n$ is not divisible by $\displaystyle 7$. The remainder when $\displaystyle n^2$ is divided by 7 and the remainder when $\displaystyle n$ is divided by $\displaystyle 7$ are each equal to $\displaystyle k$. What is $\displaystyle k$?

A. 1

B. 2

C. 4

D. 6

E. It cannot be determined from the information given.

I just looked at the middle part and concluded the answer to be 1. The only numbers I know that are equal to their squares are 0 and 1. Zero isn't available.