Tag Archives: Arthur Engel

Replacing number by positive difference in first 2n numbers where n is odd.

Posted on December 9, 2025 by Sumant Sumant

Suppose the positive integer is odd. First AL writes the numbers 1,2,..,2n on the blackboard. Then he picks any two numbers a,b, erases them and writes, instead |a-b|. Prove that an odd number will remain at the end.

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