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MathNet 2017-part-05 — 176 problems (EN–VI) Question 73

Math Olympiad Vault · MathNet 2017-part-05 — 176 problems (EN–VI)

Question 73

Let $(a_n)_{n \ge 1}$ be the sequence given by $a_1 = 2$ and $a_{n+1} = 1 + \frac{1}{a_1 a_2 \dots a_n}$, $\forall n \ge 1$.

a) Find the general term of the sequence.

b) Put $S = \sum_{k=1}^{n} \frac{2}{(k^3 + k^2)a_{2k+1}}$ in a close form and show that $S \lt 1$.