How to Check if a Given Number is Fibonacci number - Python
Fibonacci numbers are part of a famous sequence where each number is the sum of the two preceding ones, i.e. F(n) = F(n-1) + F(n-2). The sequence starts as: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ... Notice that every number is equal to the sum of its previous 2 numbers. In this article, we will learn how to identify if a given number belongs to the Fibonacci series or not. Examples : Input: 8 Output: Yes Input: 31 Output: No Fibonacci Number Check Using a Mathematical Property A number n is a Fibonacci number if and only if one or both of ( 5*n² + 4) or (5*n² – 4) is a perfect square . The above mathematical expression is derived from the closed-form expression of Fibonacci numbers (Binet’s Formula) and some number theory. It’s fast and doesn’t require generating the Fibonacci sequence. Let's look at the code implementation in Python: import math def is_perfect_sq ( x ): s = int ( math . sqrt ( x )) return s * s == x def is_fibonacci ( n ): ...
