• Trouble understanding the example (or rusty math)

Question related to mission The Good Radix

Hi everyone,

You are given some number n written as a string with the radix equal to k (1 < k < 37). We know that our number is divisible by (k - 1) without a remainder.

Ok so far.

For example: n = "18". As we can see, k should be greater than 8.

How can we see this?