The number of functions f from {1, 2, 3, ...., 20} onto {1, 2, 3, ...., 20} such that f(k) is a multiple of 3, whenever k is a multiple of 4, is :

Question

6⁵ $ \times $ (15)!

5⁶ $ \times $ 15

(15)! $ \times $ 6!

5! $ \times $ 6!

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