public List<string> output = new List<string>();
List<string> newNumeralSystem(char number) {
    string Alph = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    char[]a = new char[25];
    a =Alph.ToCharArray();
    int ac = Array.IndexOf(a,number);
    for( int x = 0 ; x > 25 ;x++)
    {
        int m = ac - x;
        if(m != 0)
        {
            //output[x] = string.Format(a[m] +"+"+ a[x]);
            output.Add(new string(){a[m] +"+"+ a[x]});

        }
    }
      return output;
}