You probably wouldn't say "interesting" in your example. You could say instead "it will interest us", or "we will be interested in [sth] e.g. the last non-zero term...". If something is "interesting", you may not necessarily want to do anything about your interest. Your interest could be quite small or temporary. However, if something specific is "of interest", you tend to take an active interest in it. Or if you are "interested in something", it is a more general interest and so you may take a regular interest in it. So although the ideas are synonymous to some extent, there are small shades of difference in usage and meaning.

Let's say that I have no idea whether you care about the history of the English language. I might say to you "Bill Bryson wrote a very interesting book entitled 'The Mother Tongue: English and How It Got That Way.' As a matter of fact, he's a brilliant writer of nonfiction, and I've found every one of his books to be interesting." Now, let's say that I happened to know that you were interested in the history of the English language. In that case, I would say "If you don't know it already, you would probably find this book to be of interest."