326. Power of Three

Given an integer, write a function to determine if it is a power of three.

Follow up:
Could you do it without using any loop / recursion?

javascript：

/**
 * @param {number} n
 * @return {boolean}
 */
var isPowerOfThree = function(n) {
    var num=Math.log(n)/Math.log(3);
    var num1=Math.abs(num-Math.round(num));
    if(num1<=0.00000000001)
    {
        return true;
    }
    else return false;
};