Fibonacci Practice

class Main {
    public static void main(String[] args) {
        System.out.println("Hello World!");
        System.out.println( fibNumRecur( 20));
        System.out.println(fibNum(20));
        // int ans = (int) Math.pow(5,2);

System.out.println(fibNumWhileLoop(5));
    }
    
    //How to form the Fibonacci series using recursion ? (Solution)
    public static int fibNumRecur(int num){
         if(num<0){
      throw new IllegalArgumentException("num should be non-negative");
         }
        
        if(num == 0){
        return 0;
        }
        if (num ==2 || num ==1){
            return 1;
        }
       
        return  fibNumRecur(num -1) + fibNumRecur(num-2);
    }
    
      public static int fibNum(int num){
          
          
          double a = ((Math.pow((1+ Math.sqrt(5)),num))-(Math.pow((1- Math.sqrt(5)),num)))/(Math.pow(2,num)*Math.sqrt(5));
        
 
       
        return  (int)a;
    }
    
    //In-progress.
     public static int fibNumWhileLoop(int num){
         
         int a = 0;
         
         while(a<=num){
           
                 System.out.println(a);
                 a++;
                 
             }
             
        
         
         
         return a;
     }
}