After 5 divisions, how many cells are there?

Depends on the starting number of cells. For all non-one original number of cells, the equation is x^y, where x is the starting number of cells, and y is the number of divisions. You have specified that y=5, so the equation is simply x^5. For one original starting cell, just do the first iteration yourself - or in math terms, do y-1=y and x=2, then do x^y.