Check If a Number Belongs to the Fibonacci Sequence in Python

Program Overview

This Python program reads an integer from the user and checks whether it is part of the Fibonacci sequence.
The Fibonacci sequence starts with 0 and 1, and each subsequent number is the sum of the previous two.

Python Code:

# Read input number from user
n = int(input("Enter a number: "))

# Check if the number is in the Fibonacci sequence
a, b = 0, 1
found = False

while a <= n:
    if a == n:
        found = True
        break
    a, b = b, a + b

# Display result
if found:
    print(f"{n} is a Fibonacci number.")
else:
    print(f"{n} is not a Fibonacci number.")

Sample Output:

Enter a number: 13  
13 is a Fibonacci number.

Enter a number: 14  
14 is not a Fibonacci number.

Step-by-Step Explanation:

- The program starts with a = 0 and b = 1
- It generates Fibonacci numbers until it reaches or exceeds n
- If n matches any generated value, it is part of the sequence
- Otherwise, the loop ends and the program reports that n is not in the sequence