A prime number (or a prime) is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number.
For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 6 is composite because it is the product of two numbers (2 × 3) that are both smaller than 6. Primes are central in number theory because of the fundamental theorem of arithmetic: every natural number greater than 1 is either a prime itself or can be factorized as a product of primes that is unique up to their order.
using System;
namespace Program
{
class Program
{
public static void Main()
{
int num;
int k;
k = 0;
Console.Write("Enter a Number: ");
num = Convert.ToInt32(Console.ReadLine());
for (int i = 1; i <= num; i++)
{
if (num % i == 0)
{
k++;
}
}
if (k == 2)
{
Console.WriteLine("Entered Number is a Prime Number and the Largest Factor is {0}", num);
}
else
{
Console.WriteLine("Not Prime!");
}
Console.ReadLine();
}
}
}
Output
