Continuing your idea, for any natural , . This is checked directly. (This is also a way to find the sum of a geometric progression.)
I got this from the exercise in the introductory chapter of Velleman's "How to Prove It."
Exercise 1b: Find an integer
and is divisible by .
I have got , such that and that
is too large to handle.
is a foreign language to me. I don't know how to proceed from here.
Someone please help.