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Turkey NMO 2006 1st Round - P12 (Combinatorics)

Source:

February 2, 2013

Problem Statement

In how many different ways can the set {1,2,,2006}\{1,2,\dots, 2006\} be divided into three non-empty sets such that no set contains two successive numbers?
<spanclass=latexbold>(A)</span> 32006322006+1<spanclass=latexbold>(B)</span> 220052<spanclass=latexbold>(C)</span> 32004<spanclass=latexbold>(D)</span> 320051<spanclass=latexbold>(E)</span> None of above <span class='latex-bold'>(A)</span>\ 3^{2006}-3\cdot 2^{2006}+1 \qquad<span class='latex-bold'>(B)</span>\ 2^{2005}-2 \qquad<span class='latex-bold'>(C)</span>\ 3^{2004} \qquad<span class='latex-bold'>(D)</span>\ 3^{2005}-1 \qquad<span class='latex-bold'>(E)</span>\ \text{None of above}