Looking for solution in Simulink

I looking for block in Simulink to make some recursion, for example:

I want calculate A_(k+1) = 2 * A开发者_JAVA技巧_(k) , where k = 1,2,3,4 and A_(1) = 3.

How to make something like this ? I only find initial values in integrator :/

You might need an Integer Delay.