MathDB
sequence with many null terms

Source: RMO District 2005, 9th Grade, Problem 4

March 5, 2005
algebra proposedalgebra

Problem Statement

Let {ak}k1\{a_k\}_{k\geq 1} be a sequence of non-negative integers, such that aka2k+a2k+1a_k \geq a_{2k} + a_{2k+1}, for all k1k\geq 1. a) Prove that for all positive integers n1n\geq 1 there exist nn consecutive terms equal with 0 in the sequence {ak}k\{a_k\}_k; b) State an example of sequence with the property in the hypothesis which contains an infinite number of non-zero terms.