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Inequality on sequence

Source: Vietnam TST 2021 P1

April 1, 2021
number theoryinequalities

Problem Statement

Define the sequence (an)(a_n) as a1=1a_1 = 1, a2n=ana_{2n} = a_n and a2n+1=an+1a_{2n+1} = a_n + 1 for all n1n\geq 1.
a) Find all positive integers nn such that akn=ana_{kn} = a_n for all integers 1kn1 \leq k \leq n. b) Prove that there exist infinitely many positive integers mm such that akmama_{km} \geq a_m for all positive integers kk.