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Team Selection Test

Turkey number theory

Problem

Two distinct positive integers are called relatively consistent if the larger one can be written as a sum of some distinct positive divisors of the other one. Show that there exist positive integers such that any two of them are relatively consistent.
Solution
By inducting on , we show that there exist relatively consistent distinct positive integers.

, and hence and is a consistent pair.

Now let be relatively consistent distinct positive integers. Then for any given there exist distinct positive divisors of , say , such that . Note that for any positive integer , we have that are distinct divisors of and their sum is equal to . Therefore, are relatively consistent for every positive integer .

Let be an integer greater than , and consider , , . By the observation above, , are relatively consistent. Note that by the induction hypothesis, for any given there exist positive divisors of , say , such that . Then, because of the choice of , we see that are distinct divisors of and their sum is . Therefore, and are consistent for every . Furthermore, and are consistent as well, since .

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Alternative solution.

Let be an integer. It is easy to verify that are pairwise relatively consistent.

Techniques

Divisibility / FactorizationSums and products