MathDB
Putnam 2002 A3: average of the elements of a set is integer

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November 2, 2011
Putnamcollege contests

Problem Statement

Let NN be an integer greater than 11 and let TnT_n be the number of non empty subsets SS of {1,2,.....,n}\{1,2,.....,n\} with the property that the average of the elements of SS is an integer.Prove that Tn−nT_n - n is always even.
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