According to this formula there are at any moment in our galaxy alone 50,000,000 different civilizations which are either trying to get in touch with us or waiting for a sign from other planets.
The terms of the Green Bank Formula take into account all the aspects in question, but in addition the scientists allotted two values to each term: a normal value admissible according to our present state of knowledge and an absolute minimum value.

N=R+FpNeFlFiFeL

In this formula:

R+ = the average annual number of new stars that are like our sun;

Fp = the number of stars with possible living beings;

Ne = the average number of planets which orbit the ecosphere of thier sun and so have adequate for the development of life by human standards;

Fl = the number of planets favored in this way on which life has actually developed;

Fi = the number of planets which are populated by intelligences with thier own ability to act during the lifetime of thier sun;

Fe = the number of planets inhabited by intelligences that have already developed technical civilization;

L = the lifespan of a civilization, for only very long lasting civilizations could encounter each other, given the vast distances in the universe.

If we take the lowest possible figures for all terms in this formula we get: N=40.
But if we take the admissable maximum value, we get N=50,000,000.

"Chariots of the Gods" Erich Von Daniken Chpt 11, pg. 162


The Green Bank, WV. Observatory has a website.