The number of potential interactions is (n 2) or nC2, which is quadratic. Here's a plot: https://www.wolframalpha.com/input/?i=plot+Binomial%5Bn%2C+2%5D+for+n%3

The number of potential interactions is (n 2) or nC2, which is quadratic. Here's a plot: https://www.wolframalpha.com/input/?i=plot+Binomial%5Bn%2C+2%5D+for+n%3D1+to+1000 https://www.wolframalpha.com/input/?i=plot+Binomial%5Bn%2C+2... Obviously this is the simplest possible way to look at it, not modeling how many of those people actually come in contact with one another, the probability of transmission, etc.