create false 'enumerable' type

listify.cs

public class Listify
{
    public int Start { get; }
    public int End { get; }
    public Listify(int start, int end)
    {
        Start = start;
        End = end;
    }

    public int this[int index]
    {
        get {
            var value = start + index;
            if (value > end) throw new IndexOutOfRangeException();
            return value;
        }
    }
}