The hash is a cryptographically random number. For it to be successful, it must start with seventeen zeros (base 16). The chance of a random number starting lik

The hash is a cryptographically random number. For it to be successful, it must start with seventeen zeros (base 16). The chance of a random number starting like that is 1 in 16^17, which is about equal to 1 in 3 x 10^20. I can't reproduce the calculation from the article that got 1.4 x 10^20. But it does say "approximately 17 zeros" so maybe it really meant "the first 16 hex digits must be zero and the 17th must be either zero or one". That would give close to the right numbers, if I haven't messed up.