Determining the minimum number of piRNA loci per kb. P
(blue points) refers to the probability to observe n hits (n∈ℕ) per kb. f(x) (yellow line) defines the function which extends the probabilities to positive rational numbers. P(x≥k) is the probability to observe at least k hits per kb (k∈ℝ). r = number of putative piRNA loci/size of piRNA encoding region [nt].