Convert a result (integer number) to a power of 10

I was writing a program to factorize a number given, with the goal being computing the maximum factorial that will fit in an unsigned long long data type.

That's the code. With it i can factorize numbers up to 65.

#include <iostream>
#include <libcork/core.h>

using namespace std;

int main() 
{
    unsigned long long numero;
    unsigned long long factorial=1;

    cout << "inserisci numero da fattorizzare ---> ";
    cin >> numero;
    cout <<"\n";

    for (unsigned long long i=1; i <= numero; i++)
    {
        factorial = factorial*i;
    }
        

    cout << factorial;
}

But while i was writing it, i thought, "couldn't i make the maximum number bigger by converting the result to a power of 10?"

The question makes sense to me, but i do not know how to apply the concept in c++

Thanks in advance :)