var numbers = new int[] { 2, 4, 5, 1, 6, 8, 2, 0, 4, 3, 4, 1, 5, 9, 7, 0, 2, 4, 8, 9 };

var pageNumber = 2;
var itemCountPerPage = 6;

var paginable = numbers.ToPaginable(pageNumber, itemCountPerPage);

foreach(var t in paginable)
{
    Console.WriteLine($"{t.ItemNumber}, {t.Item}");
}

//output
1, 2
2, 0
3, 4
4, 3
5, 4 
6, 1