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Found problems: 1

2015 NIMO Problems, 5
Tags: binary trees , counting , subset
Compute the number of subsets $S$ of $\{0,1,\dots,14\}$ with the property that for each $n=0,1,\dots, 6$, either $n$ is in $S$ or both of $2n+1$ and $2n+2$ are in $S$. [i]Proposed by Evan Chen[/i]