Marinada '15

%V0 $$f(3) = 1$$ $$f(6) = 1$$ $$f(7) = 6$$ $$f(11) = 2$$ $$f(13) = 6$$ $$f(18) = 1$$ $$f(21) = 6$$ $$f(22)*f(23) = ?$$