Problem

Source: Macedonian National Olympiad 2022 P1

Tags: Sequence, Inequality, national olympiad, algebra



Let $(x_n)_{n=1}^\infty$ be a sequence defined recursively with: $x_1=2$ and $x_{n+1}=\frac{x_n(x_n+n)}{n+1}$ for all $n \ge 1$. Prove that $$n(n+1) >\frac{(x_1+x_2+ \ldots +x_n)^2}{x_{n+1}}.$$ Proposed by Nikola Velov