MathDB
2021 Team P10

Source:

March 2, 2021
combinatorics

Problem Statement

How many functions f:{1,2,3,…,7}→{1,2,3,…,7}f:\{1,2,3, \ldots, 7\} \rightarrow \{1,2,3, \ldots, 7\} are there such that the set F={f(i):i∈{1,…,7}}\mathcal{F} = \{f(i) : i\in\{1,\ldots, 7\}\} has cardinality four, while the set G={f(f(f(i))):i∈{1,…,7}}\mathcal{G} = \{f(f(f(i))) : i\in\{1,\ldots, 7\}\} consists of a single element?
Proposed by Sam Delatore
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