Should be 1 - (1 - P0) ^ (N - 1)
Also, when you have to use such formulae, you are being very pessimistic;
the Drake equation assumes the result is very close to one and then tries
to predict how many will exist, whereas this assumes that there is a real
risk that we are the only ones.
Both are subject to unquantified parameters; this one only has two
whereas Drake's has multiple ones, so at least one can judge which factors
are wild guesses and which are known with some degree of confidence.
> Aczel is a genius. I have often had the same thoughts, but didn't have the
It's high school (A level) probability theory.