using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        string filter = "1, 2, 3,4 ,  5,,a2,,a, uishcuiahca";

        var filterIds = filter?.Split(",").Select(s => long.TryParse(s.Trim(), out var id) ? id : default).ToHashSet() ?? new HashSet<long>();

        foreach (long number in filterIds)

        {

            Console.WriteLine(number);

        }

​

        Console.WriteLine(filterIds.Contains(10));

    }

}