/**

     * HailStone序列

     * n=1时，返回1；

     * n>1时且为偶数时，{n} ∪ {n / 2}

     * n>1时且为奇数时，{n} ∪ {3n + 1}

     *

     * @param n

     * @return

     */

    public static String hailStone(int n) {

        StringBuilder str = new StringBuilder();

        while (n > 1) {

            str.append(n + ", ");

            if (n % 2 == 0) {

                n = n/2;

            } else {

                n = 3 * n + 1;

            }

        }

        if (n == 1) {

            str.append(n + ", ");

        }

        return str.substring(0, str.length() - 2);

    }