how many different outcomes question

I want to find out all the different combinations of 16 different sets, for example here is what my set looks like

a-b

a-b

for just two sets i figure there are 4 different outcomes

outcome 1.

a-b

a-b

outcome 2.

b-a

b-a

outcome 3.

b-a

a-b

outcome 4.

a-b

b-a

which would be 2 x 2 =4, and if its 4 sets

a-b

a-b

a-b

a-b

I get 16 different outcomes 4 x 4=16

but for 16 sets I would think it would just be 16 X 16=256

but when writing out all the possible outcomes it seems like it would be more than that. What would be a good formula to figure out all the different outcomes or even what would the answer be, thanks