The set of numbers {9, 99, 999, 9999, ...} has some interesting properties. One of these has to do with factorization. Take any number n that isn't divisible by 2 or by 5. You will be able to find at least one number in the set that is divisible by n. Furthermore, you won't need to look beyond the first n numbers in the set.
Prove it.
(from http://www.ocf.berkeley.edu/~wwu/riddles/)
(In reply to
Need some math theory help over here by Bryan)
I agree entirely with your analysis. This is one of those problems that is (or seems to be) obvious at first glance, the the problem is the actual proof. Not being a proof guy myself, I'll tell you I thought about the same method, and left it at that.
re: Need some math theory help over here
