semiprime numbers not showing for first few values due to error in loop?

I'm to write a program that gives me the semiprimes up to some random number. I have the "formula" down but my loops skip the first couple semiprime values even though when tracing through it, I see no logical error.

#include <iostream>
using namespace std;
unsigned nthFactor(unsigned long UL, unsigned n);
unsigned numFactors( unsigned long UL);
bool isPrime ( unsigned long UL);
bool isPerfectSquare ( unsigned long UL);
bool isSemiPrime ( unsigned long UL);

int main()
{
    unsigned long cnt=0;
    unsigned long x;
    for(x=1; x<100;x++)
    {
        if(isSemiPrime(x))
        {
            cout<<x<<endl;
            cnt++;
        }
    }
    cout<<"The number of semiprimes up to "<<x<<" is "<<cnt;
}  

unsigned numFactors ( unsigned long UL) //this function takes whatever number u put into it and finds the amount of factors it has
{
    unsigned cnt=0;

    while ( nthFactor(UL,cnt++) !=0);

    return cnt-1;
}

bool isSemiPrime ( unsigned long UL)
{

    for(unsigned long x=2; x<=(UL/2); x++) //loops through all possible factors
    {
        if(UL%x==0 && numFactors(x)==1 ) //if x factors UL and x is a prime then...
        {
            if(numFactors(UL/x)==1)     //if (UL/x) is also a prime then UL is a semiprime
            return true;
        }
    }
    return false;
}