Parallel factorial

factorialPar.cpp

#include <iostream>
#include <algorithm>
#include <vector>
#include <execution>
#include <numeric>

long double Factorial(std::vector<int> & numbers)
{
    long double result = 1.0;
  	std::for_each(
		std::execution::par_unseq,
		numbers.begin(),
		numbers.end(),
		[&](auto&& item)
		{
			result *= item;
		});
    return result;
}

int main()
{
	long double result = 1.0;
	std::vector<int> numbers(800);
	std::iota(numbers.begin(), numbers.end(), 1);
	
  std::cout << "800! is " << Factorial(numbers) << std::endl;
	return 0;
}