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Coins..

Source: China Western Mathematical Olympiad 2013, problem 4

August 21, 2013
floor functioncombinatorics unsolvedcombinatorics

Problem Statement

There are nn coins in a row, n2n\geq 2. If one of the coins is head, select an odd number of consecutive coins (or even 1 coin) with the one in head on the leftmost, and then flip all the selected coins upside down simultaneously. This is a movemove. No move is allowed if all nn coins are tails. Suppose m1m-1 coins are heads at the initial stage, determine if there is a way to carry out 2m3 \lfloor\frac {2^m}{3}\rfloor moves