Odd composite Number

using System;

namespace PrimeNumber
{
    class Program
    {
        /// <summary>
        /// Verify if given number is prime.
        /// </summary>
        /// <param name="number"></param>
        /// <returns>true if number is prime, false otherwise.</returns>
        static bool IsPrimeNumber(int number)
        {
            int divisionCount = 0;
            int index_number = number;

            while (index_number > 0)
            {
                if (number % index_number == 0)
                    divisionCount++;

                index_number--;
            }

            return (divisionCount == 2);
        }

        /// <summary>
        /// Aplication entry point
        /// </summary>
        /// <param name="args"></param>
        static void Main(string[] args)
        {
            //by definition, composite odd number is a number that is not prime
            for (int number = 1; number < 100; number++)
            {
                if (IsPrimeNumber(number))
                    Console.WriteLine("prime number -> {0}", number);
                else
                    Console.WriteLine("composite odd number -> {0}", number);
            }

            Console.ReadKey();
        }
    }
}