static bool isPrime(int number)
        {

            if (number == 1) return true;
            if (number == 2) return true;
            if (number == 3) return true;
            if (number == 4) return false;

            for (int i = 2; i <= Math.Ceiling(Math.Sqrt(Convert.ToDouble(number))); i++)
            {
                if (number % i == 0)
                {
                    return false;
                }
            }

            return true;

        }

Method to Check if an int is a Prime Number

Is this Number Prime

number

C#