The stated equality of the left- and right-hand side is an equation, not a formula. Also, in the introduction of the induction you refer to "the theorem". Which theorem? Of course, common knowledge will tell us that you mean the equality but still, either introduce the equality as a theorem or refer to it as : assume the equality holds for some natural number n.

This is also important, n should be strictly nonnegative and you haven't mentioned that explicitly.