Although straightforward pyramid schemes are illegal in many countries, such "businesses" often camouflage themselves quite successfully by assuming the form of various MLM (multilevel marketing) or Network Marketing companies. Their organizers and promoters often refer to such activities as "the 21st century business", however there's nothing about them that is particular to the 21st century, for they always existed (see below), especially in times of economic uncertainty. An MLM operation normally involves the distribution of an actual product (thus legally separating itself from a straightforward pyramid scheme), but its "success" (or rather success for those who are at the top of the pyramid or close to it) is afforded by ever increasing participation of new members whose numbers grow in geometric progression.  
A Russian and Soviet science writer Yakov Isidorovich Perelman (1882-1942) authored numerous books in which he popularized physics, mathematics, mechanics and other sciences. Thus, in 1927 he published a marvel of popular mathematics entitled "Mathematics Can Be Fun". As it happens, in one of the stories presented in the book the author employs a fairly straightforward mathematics to expose how what we call today "MLM companies" operated in pre-revolutionary Russia. Please enjoy and learn: