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Good functional and set problem

Source: 2009 Jozsef Wildt International Math Competition

April 17, 2020
Setsfunction

Problem Statement

Let consider the following function set F={f  f:{1, 2, , n}{1, 2, , n}}F=\{f\ |\ f:\{1,\ 2,\ \cdots,\ n\}\to \{1,\ 2,\ \cdots,\ n\} \}
[*] Find F|F| [*] For n=2kn=2k prove that F<e(4k)k|F|< e{(4k)}^{k} [*] Find nn, if F=540|F|=540 and n=2kn=2k