Difficulty in obtaining vanity Bitcoin addresses What is the formula I can use to estimate the difficulty in generating vanity Bitcoin addresses?
The probabilities are detailed here:

https://en.bitcoin.it/wiki/Vanitygen#Difficulty_of_finding_a_vanity

"The difficult of finding a vanity address depends on its exact structure (leading letters and numbers) and how likely such an output is given the algorithms involved, which can consist of several pivots where the difficulty suddenly changes."

Difficulty can be quite easy or quite hard depending on the structure and length of the vanity portion of your address