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Almost fixed

Author: mathforces
Problem has been solved: 10 times

Русский язык | English Language



We call a function $ f: \ \{1,2,3,...,n\} \to \{1,2,...,n\} $ almost fixed if it is one-to-one and for any pair $ (x, y ) $ if the number $ x $ is divisible by $ y $, then $ f (x) $ is divisible by $ f (y) $. Find the number of almost fixed functions for $ n = 40 $. If such functions do not exist, enter 999999.





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