Iterated function of a polynomial
Source: 11th CHKMO 2009
December 15, 2008
functionalgebrapolynomialinductionalgebra proposed
Problem Statement
Let f(x) \equal{} c_m x^m \plus{} c_{m\minus{}1} x^{m\minus{}1} \plus{}...\plus{} c_1 x \plus{} c_0, where each is a non-zero integer. Define a sequence by a_1 \equal{} 0 and a_{n\plus{}1} \equal{} f(a_n) for all positive integers .
(a) Let and be positive integers with . Show that a_{j\plus{}1} \minus{} a_j is a multiple of a_{i\plus{}1} \minus{} a_i.
(b) Show that