Hoping to find the basis of this computation, I decided to track down the reference. Unfortunately, what I found was not a series of probabalistic equations, but rather an account of Hoyle saying that he computed this number. As far as I can tell, there is no publicly available documentation supporting this figure.
Abiogenesis is a mathematical impossibility.
Sir Fred Hoyle, a British astronomer and mathematician, calculated the odds of one simple bacterium arising from a primordial soup. A simple bacterium is comprised of 2,000 different functioning proteins. In turn, each protein consists of a chain of about 300 amino acids. There are 20 distinct amino acids, so the odds of one proteinated amino acid occurring in the correct sequence is one in 20. It should be stated that biological evolution has very little to do with abiogenesis.