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IMO 2000 - Shortlisted Problems Question 10

IMO Shortlist · IMO 2000 - Shortlisted Problems

Question 10

A4 (GBR). The function $F$ is defined on the set of nonnegative integers and takes nonnegative integer values satisfying the following conditions: For every $n\ge0$,

(i) $F(4n)=F(2n)+F(n)$;

(ii) $F(4n+2)=F(4n)+1$;

(iii) $F(2n+1)=F(2n)+1$.

Prove that for each positive integer $m$, the number of integers $n$ with $0\le n\lt 2^m$ and $F(4n)=F(3n)$ is $F(2^{m+1})$.