N = R * fp * ne * fl * fi * fc * L


Rate of star formation per year (R)
Fraction of stars that form planets (fp)
Number of planets hospitable to life (ne)
Fraction of these planets where life emerges (fl)
Fraction of these planets where intelligent life emerges (fi)
Fraction of these planets where interstellar communication takes place (fc)
Length of time a civilization is detectable (L)

There could be 1 detectable intelligent civilization(s) in our galaxy.