Tensorflow, how many layers does this model have?
When talking about feed forward neural networks one distinguishes between input layer, hidden layers and output layer. Usually you have a single input and output layer and one or more hidden layers.
In your case, the input layer with 20 input neurons is not explicitly mentioned in the code but its still there. Further, there is one hidden layer with 200 neurons and one output layer with a single neuron.
So I would say you have a three layer network. But maybe there are other conventions on how to count the number of layers in a feed forward neural network. Some might exclude the input layer.