asp.net 随机数字加字母字符串

public static string RandCode(int n)
    {
        char[] arrChar = new char[]{ 
'a','b','d','c','e','f','g','h','i','j','k','l','m','n','p','r','q','s','t','u','v','w','z','y','x', 
'0','1','2','3','4','5','6','7','8','9', 
'A','B','C','D','E','F','G','H','I','J','K','L','M','N','Q','P','R','T','S','V','U','W','X','Y','Z' 
};
        StringBuilder num = new StringBuilder();
        Random rnd = new Random(DateTime.Now.Millisecond);
        for (int i = 0; i < n; i++)
        {
            num.Append(arrChar[rnd.Next(0, arrChar.Length)].ToString());
        }
        return num.ToString();
    }

n 为需要字符串的长度