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In mathematics, Proizvolov's identity is an identity concerning sums of differences of positive integers. The identity was posed by Vyacheslav Proizvolov as a problem in the 1985 All-Union Soviet Student Olympiads . To state the identity, take the first 2''N'' positive integers, :1, 2, 3, ..., 2''N'' − 1, 2''N'', and partition them into two subsets of ''N'' numbers each. Arrange one subset in increasing order: : Arrange the other subset in decreasing order: : Then the sum : is always equal to ''N''2. ==Example== Take for example ''N'' = 3. The set of numbers is then . Select three numbers of this set, say 2, 3 and 5. Then the sequences ''A'' and ''B'' are: :''A''1 = 2, ''A''2 = 3, and ''A''''3'' = 5; :''B''1 = 6, ''B''2 = 4, and ''B''''3'' = 1. The sum is : which indeed equals 32. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Proizvolov's identity」の詳細全文を読む スポンサード リンク
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