How to Check if a Given Number is Fibonacci number - Python Last Updated : 28 Apr, 2025 Comments Improve Suggest changes Like Article Like Report 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: 8Output: YesInput: 31Output: NoFibonacci Number Check Using a Mathematical PropertyA 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: Python import math def is_perfect_sq(x): s = int(math.sqrt(x)) return s * s == x def is_fibonacci(n): return is_perfect_sq(5 * n * n + 4) or is_perfect_sq(5 * n * n - 4) for i in range(1, 7): if is_fibonacci(i): print(f"{i} is a Fibonacci Number") else: print(f"{i} is not a Fibonacci Number") Output1 is a Fibonacci Number 2 is a Fibonacci Number 3 is a Fibonacci Number 4 is not a Fibonacci Number 5 is a Fibonacci Number 6 is not a Fibonacci Number Explanation:1. is_perfect_sq(x):Calculates the integer square root of x.Returns True if x is a perfect square, else False.2. is_fibonacci(n):Applies the mathematical identity:A number n is Fibonacci if 5*n² + 4 or 5*n² – 4 is a perfect square.Calls is_perfect_sq() on both expressions to check this.3. Loop: Iterates through numbers 1 to 6 and prints whether each number is a Fibonacci number based on the result from is_fibonacci().Please refer this complete article on How to check if a given number is Fibonacci number? for more details! Comment More infoAdvertise with us Next Article How to Check if a Given Number is Fibonacci number - Python K kartik Follow Improve Article Tags : Python Practice Tags : python Similar Reads Nth multiple of a number in Fibonacci Series in Python Our task is to find the nth multiple of a number in the Fibonacci series which involves identifying Fibonacci numbers that are exactly divisible by a given number m. This means we will check each Fibonacci number one by one and select only those that are multiples of m. Once we find the nth such num 4 min read Check If Value Is Int or Float in Python In Python, you might want to see if a number is a whole number (integer) or a decimal (float). Python has built-in functions to make this easy. There are simple ones like type() and more advanced ones like isinstance(). In this article, we'll explore different ways to check if a value is an integer 4 min read Check if a given string is binary string or not - Python The task of checking whether a given string is a binary string in Python involves verifying that the string contains only the characters '0' and '1'. A binary string is one that is composed solely of these two digits and no other characters are allowed. For example, the string "101010" is a valid bi 3 min read Implement IsNumber() function in Python In this article we will see how to implement isNumber() method using Python. This method takes in a string as input and returns True or False according to whether the string is a number or not. Examples: Input : "12345" Output : True Input : "-12345" Output : True Input : "abc" Output : False Approa 2 min read Check If String is Integer in Python In this article, we will explore different possible ways through which we can check if a string is an integer or not. We will explore different methods and see how each method works with a clear understanding.Example:Input2 : "geeksforgeeks"Output2 : geeksforgeeks is not an IntigerExplanation : "gee 4 min read Like