Java: Check if a given number is Fibonacci number or not

Last update on May 15 2025 13:09:10 (UTC/GMT +8 hours)

Check Fibonacci Number

Write a Java program to check if a given number is a Fibonacci number or not.

Sample Solution:

Java Code:

import java.util.*;

class solution {
  static boolean isPerfectSquare(int x)
    {
       int s = (int) Math.sqrt(x); 
       return (s*s == x);
     }
  
   static boolean isFibonacci(int x)
      {
         return isPerfectSquare(5*x*x + 4) ||
           isPerfectSquare(5*x*x - 4);
     }

    public static void main(String[] args)
    {   
      Scanner scan = new Scanner(System.in);
      System.out.print("Input a number: ");
      int n = scan.nextInt();	       
	  if (n>0)
		{	
		 System.out.println("Is Fibonacci number? "+isFibonacci(n)); 
		}         
   }
}

Sample Output:

Input a number:  55
Is Fibonacci number? true

Flowchart:

$Flowchart: Check if a given number is Fibonacci number or not.$

For more Practice: Solve these Related Problems:

Write a Java program to check if a number is in the Fibonacci sequence using an iterative approach.
Write a Java program to determine if a given number is Fibonacci by verifying if 5*n²+4 or 5*n²-4 is a perfect square.
Write a Java program to recursively generate Fibonacci numbers until exceeding a given input and then check for equality.
Write a Java program to use a mathematical formula to decide whether a number is Fibonacci and output a boolean result.

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