string str = "123456";
string[] arr = str.MySplit(2);
static string[] MySplit(this string str, int count) {
var list = new List<string>();
int length = (int)Math.Ceiling((double)str.Length / count);
for(int i = 0; i < length; i++) {
int start = count * i;
if(str.Length <= start) {
break;
}
if(str.Length < start + count) {
list.Add(str.Substring(start));
} else {
list.Add(str.Substring(start, count));
}
}
return list.ToArray();
}