using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var groupSize = 4;

        // The characters 'a' - 'z'.

        var source = Enumerable.Range(0, 26).Select(i => (Char)('a' + i));

        var groups = source.Select((x, i) => new

        {

        Item = x, Index = i

        }

​

        ).GroupBy(x => x.Index / groupSize, x => x.Item);

        foreach (var group in groups)

            Console.WriteLine("{0}: {1}", group.Key, String.Join(", ", group));

    }

}