What does your function return for negative numbers like -3? Read the description again. Also, printing the input would help you debug your code.

First of all, your code is almost unreadable because it's all on one line. Format it properly as shown here https://docs.codewars.com/references/markdown/#code-block

Secondly, from description:

a prime number is a natural number greater than 1

Why are you bothering with negative numbers then?

It also looks like you got some flawed logic in your else statement, but it's just a guess because, again, your code is unreadable right now.