Introduction

In the previous article, we have understood the mathematical expression to find n^th Fibonacci number. In this article, we will learn to write python code to check whether the given number is Fibonacci number or not. The number is said to be a Fibonacci number if the expression (5*n*n + 4) or (5*n*n – 4) or both is a perfect square. The first few Fibonacci numbers are:

0, 1, 1, 2, 3, 5, 8, 13, …….

Program

import math
n = int(input("Please enter the integer value to check Fibonacci number: "))


def check_perfect_square(m):
    n = int(math.sqrt(m))
    return n*n == m
   
def check_fibo(m):
    return check_perfect_square(5*m*m + 4) or check_perfect_square(5*m*m - 4)
if(check_fibo(n) == True):
    print( n," is Fibonacci number")
else:
    print( n," is not Fibnacci number")

Output

Explanation

In the above python code, we have created a variable n, function check_perfect_square()  and check_fibo().The function check_perfect_square() returns the value True if the given number is perfect square and the integer value is passed to function check_fibo(). If the expression (5*m*m + 4) or (5*m*m – 4) holds true for given input then the number is a Fibonacci number.