Exponentially growth.
Let’s say one person starts with the flu. After the first day, there are suddenly
1 x 2 = 4 people sick
And the rest of the days just explode in magnitude:
Day 2: 1 x 2 x 2 = 8 people sick
Day 3: 1 x 2 x 2 x 2 = 16 people sick
Day 4: 1 x 2 x 2 x 2 x 2 = 32 people sick
Etc.
You can rewrite all that repeated multiplication as *exponents*, which is why we call it exponential growth.
Day 1: 1 x 2^1 = 4
Day 2: 1 x 2^2 = 8
Day 3: 1 x 2^3 = 16
And after n days, 1 x 2^n - or just 2^n - people would be sick.
