Python program to check whether a number is Fibonacci or not

    
        import math

        def isPerfectSquare(num):
            square_root = int(math.sqrt(num))
            return square_root * square_root == num

        def isFibonacciNumber(n):
            # A number is a Fibonacci number if one of the conditions is true
            if isPerfectSquare(5 * n * n + 4) or isPerfectSquare(5 * n * n - 4):
                return True
            else:
                return False

        # Example usage:
        number_to_check = int(input("Enter a number to check if it's a Fibonacci number: "))

        if isFibonacciNumber(number_to_check):
            print(f"{number_to_check} is a Fibonacci number.")
        else:
            print(f"{number_to_check} is not a Fibonacci number.")
    

    
        Enter a number to check if it's a Fibonacci number: 12
        12 is not a Fibonacci number.
    

    
        Enter a number to check if it's a Fibonacci number: 21
        21 is a Fibonacci number.