13
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Am I on the right track? I am not sure about my reasoning...
Number of surjective functions from $A$ to $B$
$$A = \{1,2,3,4\} ; B = \{a,b,c\}$$
We must count the surjective functions, meaning the functions for which for all $b \in B$, $\exists~a \in A$ such that $f(a) = b$, $f$ being one of those...