Isn't there a mathematical equation available for researchers to calculate the probability of other worlds that have very advance races of aliens? If so, could you tell me what the equation is? Thanx

Ps: I believe the answer to the difference between t(n) and f(n) are factors of the equation I am asking for in my above posting. I'm guessing that t(n) is the total number of planets that have life as we know it In the universe. And f(n) may be the total number of planets that have very advanced technologies and culturals that are capable of space travel to other worlds.