Question 15
Find all injective functions $f : \mathbb{R} \to \mathbb{R}$ such that for every real number $x$ and every positive integer $n$,
$$
\left| \sum_{i=1}^{n} i \left( f(x+i+1) - f(x+i) \right) \right| \lt 2016
$$
$$
\left| \sum_{i=1}^{n} i \left( f(x+i+1) - f(x+i) \right) \right| \lt 2016
$$