title: How many hidden layers are there in a Deep Neural Network
body: <p>can anybody tell me "usually" how many layers does a Deep Neural Network have? How deep is deep enough?</p>
  
  <p>To my knowledge, it is still difficult to say the specific number of the hidden layers. But can anyone tell me, like some examples, how many hidden layers will researchers, developers use in their deep learning projects?</p>
  
  <p>Many thanks.</p>