How many consecutive cell divisions are required to form the adult human body from the single cell zygote?
Sounds like just a math problem if you allow that cells dying and different rates of division are not to be accounted for:

$2^N = 40 \times 10^{12}$

$log_2(40 \times 10^{12}) = N$

$N = 45.185$

so 45 or so divisions. 

is that what you are looking for?