Okay, so not the stuff about x(x-1) and x((x-1)!) which thoroughly hurt my brain, but about it having to be an underestimate! My husband was my second sexual partner, however I was his fifth, and I'm sure it differs in that respect with each sexual couple.. it would almost always have to be an underestimate.
So.. how does that math work out? If I have two partners, and each of those has had two partners, I've actually been exposed to 4 people, surely? And three would be 9.. They seem to only be counting your own partners as one :S
So, how about that safe sex eh? And by safe, I mean basically not just jumping into bed with randoms.