The final phase of the football World Cup is played as a knockout stage: those who lose are eliminated, so at each round the number of teams is halved. The number of teams, say n, is initially a power of 2, for example n = 24 = 16. In this case, the sixteen teams play in the octofinals from which eight winning teams emerge that meet in the quarterfinals; the four winning teams play in the semifinals, and finally two teams play in the final from which the world champion team emerges. Note that these numbers 16, 8, 4, 2, and 1 are all powers of 2 with decreasing exponents: the last one is 20 = 1.
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