We need what is called a base case to make the recursion stop. Base cases are conditions at the start of recursive functions that terminate the calls.

Let’s look at the Fibonacci numbers . The Fibonacci numbers are a sequence of numbers starting with 0, 1. Then, each number is defined as the sum of the previous two numbers. The first few Fibonacci numbers are 0, 1, 1, 2, 3, 5, 8. More formally, we have

Fn=Fn−1+Fn−2Fn​=Fn−1​+Fn−2​

This is called a recurrence relation - it’s an equation that connects the terms together.