Expronential Growth and Decay,Please! Help 10 point?

Every twenty min the number of bacteria's doubled. Let at time t the number be n then at time (t+20min) the number will be 2n. Therefore after t+40min it will be 4n. After t+60min it will be 8n. Therefore after t+m20min the number will be (2^m)n. Therefore the equation for any time T's=n* 2^((T-t)/20min). Lets take the case when t=0min we will have n=1. Therefore the final number for T min=2^(T/20min). Therefore the equation's n(T)=2^(T/20min).