This is pretty much it. I'd make an intuitive guess that the average number of friends of friends is Sum((F_n)^2) / Sum(F_n), where F_n is the number of friends

This is pretty much it. I'd make an intuitive guess that the average number of friends of friends is Sum((F_n)^2) / Sum(F_n), where F_n is the number of friends that person n has.