MathDB
Tuymaada 2010, Junior League, Problem 4

Source:

July 18, 2010
combinatorics unsolvedcombinatoricsinvariant

Problem Statement

On a blackboard there are 20102010 natural nonzero numbers. We define a "move" by erasing xx and yy with y0y\neq0 and replacing them with 2x+12x+1 and y1y-1, or we can choose to replace them by 2x+12x+1 and y14\frac{y-1}{4} if y1y-1 is divisible by 4.
Knowing that in the beginning the numbers 20062006 and 20082008 have been erased, show that the original set of numbers cannot be attained again by any sequence of moves.