Considering that factorial of 1e6 has about 18e6 bits (and factorial of 1e3 has 8.5e3 bits)? Yes, any factorial that doesn't have a huge amount of bits will be

Considering that factorial of 1e6 has about 18e6 bits (and factorial of 1e3 has 8.5e3 bits)? Yes, any factorial that doesn't have a huge amount of bits will be fast enough to calculate that there's not much point to parallelizing it.