IMO Shortlist 2016 problem N1
Dodao/la:
arhiva3. listopada 2019. For any positive integer $k$, denote the sum of digits of $k$ in its decimal representation by $S(k)$. Find all polynomials $P(x)$ with integer coefficients such that for any positive integer $n \geq 2016$, the integer $P(n)$ is positive and $$S(P(n)) = P(S(n)).$$
Izvor: https://www.imo-official.org/problems/IMO2016SL.pdf