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sum of digits of N, 5N All-Russian MO 2005 Regional 8.5 9.5.

Source:

August 26, 2024
number theorysum of digitsEven

Problem Statement

It is known that the sum of the digits of the natural number NN is 100100, and the sum of the digits of the number 5N5N is 5050. Prove that NN is even.
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