How many numbers in the number set $16,17,18,19$ and $20$ have more than $3$ factors? 
Overseas Competition->Knowledge Point->Number Theory Modules->Factors and Multiples
$$16$$：$$1$$, $$2$$, $$4$$, $$8$$, $$16$$  $$17$$：$$1$$, $$17$$  $$18$$：$$1$$, $$2$$, $$3$$, $$6$$, $$9$$, $$18$$  $$19$$：$$1$$, $$19$$  $$20$$：$$1$$, $$2$$, $$4$$, $$5$$, $$10$$, $$20$$ 