Remove duplicates from an interger array

int[] a = { 1, 3, 2, 5, 6, 1, 2, 3 };
string s =",";
for (int i = 0; i < a.Length - 1; i++)
{
if (!s.Contains("," + a[i].ToString() + ","))
{
s += "," + a[i].ToString() + ",";
}
}
string ss = s.Replace(",,",",");
string sss = ss.Substring(1,ss.Length-2).Trim();
string[] aa = ss.Split(',');
int[] n=new int[ss.Split(',').Length-2];
for (int i=1;i<aa.Length-1;i++)
{
        if (aa[i].Replace(",", "")!="")
        n[i-1] = int.Parse(aa[i].Replace(",",""));
}
return n;