The endpoints of the Cantor set can be written as $0.a_1a_2a_3\dots a_{n+1}$ base 3

Question

I want to show that the endpoints of the Cantor set can be written as $0.a_1a_2a_3\dots a_{n+1}$ base 3, where each $a_k$ is 0 or 2, except $a_{n+1}$, can be 1 or 2. I know that any element in the Cantor set can be written in base 3 without using the digit 1, but I don't know about the endpoints. How would I go about showing this? I'm not sure where to start