For $n \ge 2$, let $a_1, a_2,... a_n$ be reals such that $a_1 + a_2 + ...+ a_n = n^n - 1$. Show that $$a^2_1+\frac{a^2_2}{1 + a^2_1}+ ... +\frac{a^2_n}{1 + a^2_1+ a^2_2+ ...+ a^2_{n-1}} > n \left( \frac{n^2}{\sqrt[n]{n + 1}}- 1\right)$$
Problem
Source: 2021 IGMO Christmas Edition R2 #3 https://artofproblemsolving.com/community/c3685419_igmo
Tags: algebra, inequalities