static int NumberOfDividers(int number)
        {
            int counter = 0;
            for (int i = 1; i <= number; i++)
                if (number % i == 0)
                    counter++;
            return counter;

        }
        static void Main()
        {
            int counter = 0;
            for (int i = 1; i < 100000; i++)
            {
                if (NumberOfDividers(i) == NumberOfDividers(i + 1))
                    counter++;
            }
            Console.WriteLine(counter);
        }

void Main()
{
    int counter = 0;
    int current = 0;
    for (int i = 1; i < 100000; i++)
    {
        int next = NumberOfDividers(i);
        if (current == next)
        {
            counter++;
        }
        current = next;
    }
    Console.WriteLine(counter);//10585
}

static int NumberOfDividers(int number)
{
    int counter = number == 1 ? 0 : 2;

double root = Math.Sqrt(number);

int intRoot = (int)root;
    if(intRoot * intRoot  == number)
        counter++;

for (int i = 2; i < root; i++)
        if (number % i == 0)
        {
            counter +=2;//делители ходят парами. поэтому увеличиваем сразу на два.
        }
    return counter;
}