using binet's formula it fails for some tests

Ladder

class Solution {
    public int[] solution(int[] A, int[] B) {
        // write your code in Java SE 8
        int length=A.length;
        int result[]=new int[length];
        
        for(int index=0;index<length;index++){
            //using Binet's formula
            double num=A[index]+1;
            double phi= (1+Math.sqrt(5))/2; 
            result[index]=(((int)((Math.pow(phi,num)-Math.pow(1-phi,num))/Math.sqrt(5)))) & ((1 << B[index]) - 1);
        }
        return result;
        
    }

}