dual palindromic primes of n digits

gistfile1.java

  public static int count(int digits) {
    if (digits % 2 == 0) {
      return countEven(digits);
    } else {
      return countOdd(digits);
    }
  }

  public static int countEven(int digits) {
    // +1 -1
    return fun(digits / 2);
  }

  public static int countOdd(int digits) {
    int roundDown = (digits) / 2;
    return 2 * fun(roundDown) + roundDown;
  }

  public static int fun(int n) {
    return (n * n * n - 3 * n * n + 8 * n + 6)/6;
  }