using System;
using System.Linq;
using System.Collections.Generic;
 
public class Test
{
        public static void Main()
        {
            List<int> mylist = new List<int> { 10, 11, 23, 34, 56, 43 };
            List<int> newList = mylist.Select((v, i) => new { v, i })
                        .Where(x => x.v > 23)
                        .Select(x => x.i).ToList<int>();
 
            foreach (int indices in newList)
            {
                Console.WriteLine(indices); // Output is 3, 4, 5
            }
        }
}

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