Sum of even coefficients of iterated polynomial – math.stackexchange.com
hdecristo
This problem is from the undergraduate olympiad "Elon Lima".
Let $f_1(x) = x^2 + 4x + 2$ and let $f_{n+1}(x) = f(f_n(x))$ for $n \geq 1$. Let $s_n$ be the sum of coefficients of even power ...