Java: Finding the largest chain in a Collatz sequence

Question

I cannot find what's wrong for Project Euler problem #14. My first step was finding the algorithm, which worked until the numbers hit around 120000. The code broke and realized that I needed to use BigIntegers. I converted my algorithm to meet that change, but now it does not work.

I've added the System.out.print(chain_length) to assist me in where my code can potentially break.

public static void main(String[] args) {
    BigInteger target = new BigInteger("1000000");
    BigInteger n = new BigInteger("0");

    final BigInteger zero = new BigInteger("0");
    final BigInteger one = new BigInteger("1");
    final BigInteger two = new BigInteger("2");
    final BigInteger three = new BigInteger("3");
    final BigInteger ten = new BigInteger("10");

    int greatest_index = 0;
    int greatest_length = 0;
    int chain_length = 0;

    BigInteger i = new BigInteger("2");
    for(i.equals(2) ; i.compareTo(target) == -1 ; i = i.add(one)) {
        n = i;
        chain_length = 1;
        while(n.compareTo(one) == -1) {
            chain_length++;
            if(n.mod(ten).equals(zero) == true){//even
                n = n.divide(two);
            }else{//odd
                n = n.multiply(three);
                n = n.add(one);
            }
            if(n.equals(one) == true && chain_length > greatest_length){
                greatest_length = chain_length;
                greatest_index = i.intValue();
            }
        }
        System.out.println(chain_length);
    }
    System.out.println(greatest_index);        
}

Answer 1

To test if a number is even you use modulo 2, not 10. Change this line:

if(n.mod(ten).equals(zero) == true){//even

To this:

if(n.mod(two).equals(zero)) { //even

I also removed the unnecessary == true.