GO Classes Weekly Quiz 12 | Discrete Mathematics | Group Theory, Functions | Question: 4

Answer 1

We know that the set $\{1, 2, \dots , n - 1\}$ is a group under multiplication modulo $n$ if and only if $n$ is a prime number.

so, the minimum possible value of $n$ between $20$ and $30$ is $23.$

Answer 2

Here i have taken an example and tried to explain how to make it group under multiplication modulo.