MathDB
Putnam 2000 A6

Source:

September 6, 2011
Putnamalgebrapolynomialmodular arithmeticinductionRational Root Theoremfunction

Problem Statement

Let f(x)f(x) be a polynomial with integer coefficients. Define a sequence a0,a1,a_0, a_1, \cdots of integers such that a0=0a_0=0 and an+1=f(an)a_{n+1}=f(a_n) for all n0n \ge 0. Prove that if there exists a positive integer mm for which am=0a_m=0 then either a1=0a_1=0 or a2=0a_2=0.