Yes - based on an estimate that probability of the pattern occuring is 0.1, the probability of it happening 50 times in a row is (0.1)^50. To be honest I don't understand your description of the pattern, but as long as it's well defined this probability calculation should be good. However, this assumes the pattern you describe is not based on what you see in the left rows - i.e. the pattern is something pre-defined.