using System;
using System.Linq;
int[] numbers = { 2, 3, 5, 7, 11, 13, 17 };
var contain5 = numbers.Contains(5);
//contain5 is True
var index5 = numbers.ToList().IndexOf(5);
//index5 is 2
var contain10 = numbers.Contains(10);
//contain10 is False
Console.WriteLine("{0}, {1}, {2}", contain5, index5, contain10);