Take any two digit number, reverse its digits, and subtract the
smaller number from the larger. For example $$42-24=18$$ I've tried
this a few times and I never seem to end up with a prime number.
Try some examples of your own. Do you ever end up with a prime
Can you prove that you will never
end up with a prime?
What happens when I do the same with a three digit number?
What about a four digit number?
What about a five, six, seven, ... $n$ digit number?
Can you justify your findings?