yes, limit is a VERY important topic.
the uppercase N is some natural number and n is some large number bigger than N that satisfies
the formal defination goes like this:
a sequence has a limit L if, for every there exists a Natural number N such that whenever
i.e. (a_n) ->
essentially what you are doing is making the sequence as close to its limit L by taking n large enough. This lowercase n has to be bigger than some uppercase N which is a natural number.
Hope that helps!
if you have any qn post back.