Nonzero: The Logic of Human Destiny is a 1999 book by Robert Wright, in which the author argues that biological evolution and cultural evolution are shaped and directed first and foremost by "non-zero-sumness" i.e., the prospect of creating new interactions that are not zero-sum.
Without using computer programs, can we find the last non-zero digit of $$(\dots((2018\underset{! \text{ occurs }1009\text{ times}}{\underbrace{!)!)!\dots)!}}$$?
What I know is that the last non-zero digit of ##2018!## is ##4##, but I do not know what to do with that ##4##.
Is it useful that...