Proper Definition for Recursive Series

recursion

Your confusion does make sense, but so does the equation.

Depending on where you are and what academic field you're studying in, the set of natural numbers may or may not include 0 (here's a link to a wikipedia article with an ISO standard stating 0 is included: https://en.wikipedia.org/wiki/ISO_31-11). This is a matter of lack of standardization of definition.

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