Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2014/paper-1/19/c/i/solution

There is an indexing defect in the original PDF: the term at is undefined because . Thus the series as literally indexed is not defined. The natural finite-index repair is to start at , and that repaired series still diverges.
Indeed, for the terms are positive and
They eventually increase at a geometric rate and do not tend to zero. Since the terms of a convergent series tend to zero, no choice of a finite replacement for the missing first term could make the tail converge.

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